Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

7 files changed, 1315 insertions, 0 deletions

diff --git a/Documentation/driver-api/soundwire/bra.rst b/Documentation/driver-api/soundwire/bra.rst
new file mode 100644
index 000000000..c08ab2591
--- /dev/null
+++ b/Documentation/driver-api/soundwire/bra.rst
@@ -0,0 +1,336 @@
+==========================
+Bulk Register Access (BRA)
+==========================
+
+Conventions
+-----------
+
+Capitalized words used in this documentation are intentional and refer
+to concepts of the SoundWire 1.x specification.
+
+Introduction
+------------
+
+The SoundWire 1.x specification provides a mechanism to speed-up
+command/control transfers by reclaiming parts of the audio
+bandwidth. The Bulk Register Access (BRA) protocol is a standard
+solution based on the Bulk Payload Transport (BPT) definitions.
+
+The regular control channel uses Column 0 and can only send/retrieve
+one byte per frame with write/read commands. With a typical 48kHz
+frame rate, only 48kB/s can be transferred.
+
+The optional Bulk Register Access capability can transmit up to 12
+Mbits/s and reduce transfer times by several orders of magnitude, but
+has multiple design constraints:
+
+  (1) Each frame can only support a read or a write transfer, with a
+      10-byte overhead per frame (header and footer response).
+
+  (2) The read/writes SHALL be from/to contiguous register addresses
+      in the same frame. A fragmented register space decreases the
+      efficiency of the protocol by requiring multiple BRA transfers
+      scheduled in different frames.
+
+  (3) The targeted Peripheral device SHALL support the optional Data
+      Port 0, and likewise the Manager SHALL expose audio-like Ports
+      to insert BRA packets in the audio payload using the concepts of
+      Sample Interval, HSTART, HSTOP, etc.
+
+  (4) The BRA transport efficiency depends on the available
+      bandwidth. If there are no on-going audio transfers, the entire
+      frame minus Column 0 can be reclaimed for BRA. The frame shape
+      also impacts efficiency: since Column0 cannot be used for
+      BTP/BRA, the frame should rely on a large number of columns and
+      minimize the number of rows. The bus clock should be as high as
+      possible.
+
+  (5) The number of bits transferred per frame SHALL be a multiple of
+      8 bits. Padding bits SHALL be inserted if necessary at the end
+      of the data.
+
+  (6) The regular read/write commands can be issued in parallel with
+      BRA transfers. This is convenient to e.g. deal with alerts, jack
+      detection or change the volume during firmware download, but
+      accessing the same address with two independent protocols has to
+      be avoided to avoid undefined behavior.
+
+  (7) Some implementations may not be capable of handling the
+      bandwidth of the BRA protocol, e.g. in the case of a slow I2C
+      bus behind the SoundWire IP. In this case, the transfers may
+      need to be spaced in time or flow-controlled.
+
+  (8) Each BRA packet SHALL be marked as 'Active' when valid data is
+      to be transmitted. This allows for software to allocate a BRA
+      stream but not transmit/discard data while processing the
+      results or preparing the next batch of data, or allowing the
+      peripheral to deal with the previous transfer. In addition BRA
+      transfer can be started early on without data being ready.
+
+  (9) Up to 470 bytes may be transmitted per frame.
+
+  (10) The address is represented with 32 bits and does not rely on
+       the paging registers used for the regular command/control
+       protocol in Column 0.
+
+
+Error checking
+--------------
+
+Firmware download is one of the key usages of the Bulk Register Access
+protocol. To make sure the binary data integrity is not compromised by
+transmission or programming errors, each BRA packet provides:
+
+  (1) A CRC on the 7-byte header. This CRC helps the Peripheral Device
+      check if it is addressed and set the start address and number of
+      bytes. The Peripheral Device provides a response in Byte 7.
+
+  (2) A CRC on the data block (header excluded). This CRC is
+      transmitted as the last-but-one byte in the packet, prior to the
+      footer response.
+
+The header response can be one of:
+  (a) Ack
+  (b) Nak
+  (c) Not Ready
+
+The footer response can be one of:
+  (1) Ack
+  (2) Nak  (CRC failure)
+  (3) Good (operation completed)
+  (4) Bad  (operation failed)
+
+Example frame
+-------------
+
+The example below is not to scale and makes simplifying assumptions
+for clarity. The different chunks in the BRA packets are not required
+to start on a new SoundWire Row, and the scale of data may vary.
+
+      ::
+
+	+---+--------------------------------------------+
+	+   |                                            |
+	+   |             BRA HEADER                     |
+	+   |                                            |
+	+   +--------------------------------------------+
+	+ C |             HEADER CRC                     |
+	+ O +--------------------------------------------+
+	+ M | 	          HEADER RESPONSE                |
+	+ M +--------------------------------------------+
+	+ A |                                            |
+	+ N |                                            |
+	+ D |                 DATA                       |
+	+   |                                            |
+	+   |                                            |
+	+   |                                            |
+	+   +--------------------------------------------+
+	+   |             DATA CRC                       |
+	+   +--------------------------------------------+
+	+   | 	          FOOTER RESPONSE                |
+	+---+--------------------------------------------+
+
+
+Assuming the frame uses N columns, the configuration shown above can
+be programmed by setting the DP0 registers as:
+
+    - HSTART = 1
+    - HSTOP = N - 1
+    - Sampling Interval = N
+    - WordLength = N - 1
+
+Addressing restrictions
+-----------------------
+
+The Device Number specified in the Header follows the SoundWire
+definitions, and broadcast and group addressing are permitted. For now
+the Linux implementation only allows for a single BPT transfer to a
+single device at a time. This might be revisited at a later point as
+an optimization to send the same firmware to multiple devices, but
+this would only be beneficial for single-link solutions.
+
+In the case of multiple Peripheral devices attached to different
+Managers, the broadcast and group addressing is not supported by the
+SoundWire specification. Each device must be handled with separate BRA
+streams, possibly in parallel - the links are really independent.
+
+Unsupported features
+--------------------
+
+The Bulk Register Access specification provides a number of
+capabilities that are not supported in known implementations, such as:
+
+  (1) Transfers initiated by a Peripheral Device. The BRA Initiator is
+      always the Manager Device.
+
+  (2) Flow-control capabilities and retransmission based on the
+      'NotReady' header response require extra buffering in the
+      SoundWire IP and are not implemented.
+
+Bi-directional handling
+-----------------------
+
+The BRA protocol can handle writes as well as reads, and in each
+packet the header and footer response are provided by the Peripheral
+Target device. On the Peripheral device, the BRA protocol is handled
+by a single DP0 data port, and at the low-level the bus ownership can
+will change for header/footer response as well as the data transmitted
+during a read.
+
+On the host side, most implementations rely on a Port-like concept,
+with two FIFOs consuming/generating data transfers in parallel
+(Host->Peripheral and Peripheral->Host). The amount of data
+consumed/produced by these FIFOs is not symmetrical, as a result
+hardware typically inserts markers to help software and hardware
+interpret raw data
+
+Each packet will typically have:
+
+  (1) a 'Start of Packet' indicator.
+
+  (2) an 'End of Packet' indicator.
+
+  (3) a packet identifier to correlate the data requested and
+      transmitted, and the error status for each frame
+
+Hardware implementations can check errors at the frame level, and
+retry a transfer in case of errors. However, as for the flow-control
+case, this requires extra buffering and intelligence in the
+hardware. The Linux support assumes that the entire transfer is
+cancelled if a single error is detected in one of the responses.
+
+Abstraction required
+~~~~~~~~~~~~~~~~~~~~
+
+There are no standard registers or mandatory implementation at the
+Manager level, so the low-level BPT/BRA details must be hidden in
+Manager-specific code. For example the Cadence IP format above is not
+known to the codec drivers.
+
+Likewise, codec drivers should not have to know the frame size. The
+computation of CRC and handling of responses is handled in helpers and
+Manager-specific code.
+
+The host BRA driver may also have restrictions on pages allocated for
+DMA, or other host-DSP communication protocols. The codec driver
+should not be aware of any of these restrictions, since it might be
+reused in combination with different implementations of Manager IPs.
+
+Concurrency between BRA and regular read/write
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The existing 'nread/nwrite' API already relies on a notion of start
+address and number of bytes, so it would be possible to extend this
+API with a 'hint' requesting BPT/BRA be used.
+
+However BRA transfers could be quite long, and the use of a single
+mutex for regular read/write and BRA is a show-stopper. Independent
+operation of the control/command and BRA transfers is a fundamental
+requirement, e.g. to change the volume level with the existing regmap
+interface while downloading firmware. The integration must however
+ensure that there are no concurrent access to the same address with
+the command/control protocol and the BRA protocol.
+
+In addition, the 'sdw_msg' structure hard-codes support for 16-bit
+addresses and paging registers which are irrelevant for BPT/BRA
+support based on native 32-bit addresses. A separate API with
+'sdw_bpt_msg' makes more sense.
+
+One possible strategy to speed-up all initialization tasks would be to
+start a BRA transfer for firmware download, then deal with all the
+"regular" read/writes in parallel with the command channel, and last
+to wait for the BRA transfers to complete. This would allow for a
+degree of overlap instead of a purely sequential solution. As such,
+the BRA API must support async transfers and expose a separate wait
+function.
+
+
+Peripheral/bus interface
+------------------------
+
+The bus interface for BPT/BRA is made of two functions:
+
+    - sdw_bpt_send_async(bpt_message)
+
+      This function sends the data using the Manager
+      implementation-defined capabilities (typically DMA or IPC
+      protocol).
+
+      Queueing is currently not supported, the caller
+      needs to wait for completion of the requested transfer.
+
+   - sdw_bpt_wait()
+
+      This function waits for the entire message provided by the
+      codec driver in the 'send_async' stage. Intermediate status for
+      smaller chunks will not be provided back to the codec driver,
+      only a return code will be provided.
+
+Regmap use
+~~~~~~~~~~
+
+Existing codec drivers rely on regmap to download firmware to
+Peripherals. regmap exposes an async interface similar to the
+send/wait API suggested above, so at a high-level it would seem
+natural to combine BRA and regmap. The regmap layer could check if BRA
+is available or not, and use a regular read-write command channel in
+the latter case.
+
+The regmap integration will be handled in a second step.
+
+BRA stream model
+----------------
+
+For regular audio transfers, the machine driver exposes a dailink
+connecting CPU DAI(s) and Codec DAI(s).
+
+This model is not required BRA support:
+
+   (1) The SoundWire DAIs are mainly wrappers for SoundWire Data
+       Ports, with possibly some analog or audio conversion
+       capabilities bolted behind the Data Port. In the context of
+       BRA, the DP0 is the destination. DP0 registers are standard and
+       can be programmed blindly without knowing what Peripheral is
+       connected to each link. In addition, if there are multiple
+       Peripherals on a link and some of them do not support DP0, the
+       write commands to program DP0 registers will generate harmless
+       COMMAND_IGNORED responses that will be wired-ORed with
+       responses from Peripherals which support DP0. In other words,
+       the DP0 programming can be done with broadcast commands, and
+       the information on the Target device can be added only in the
+       BRA Header.
+
+   (2) At the CPU level, the DAI concept is not useful for BRA; the
+       machine driver will not create a dailink relying on DP0. The
+       only concept that is needed is the notion of port.
+
+   (3) The stream concept relies on a set of master_rt and slave_rt
+       concepts. All of these entities represent ports and not DAIs.
+
+   (4) With the assumption that a single BRA stream is used per link,
+       that stream can connect master ports as well as all peripheral
+       DP0 ports.
+
+   (5) BRA transfers only make sense in the context of one
+       Manager/Link, so the BRA stream handling does not rely on the
+       concept of multi-link aggregation allowed by regular DAI links.
+
+Audio DMA support
+-----------------
+
+Some DMAs, such as HDaudio, require an audio format field to be
+set. This format is in turn used to define acceptable bursts. BPT/BRA
+support is not fully compatible with these definitions in that the
+format and bandwidth may vary between read and write commands.
+
+In addition, on Intel HDaudio Intel platforms the DMAs need to be
+programmed with a PCM format matching the bandwidth of the BPT/BRA
+transfer. The format is based on 192kHz 32-bit samples, and the number
+of channels varies to adjust the bandwidth. The notion of channel is
+completely notional since the data is not typical audio
+PCM. Programming such channels helps reserve enough bandwidth and adjust
+FIFO sizes to avoid xruns.
+
+Alignment requirements are currently not enforced at the core level
+but at the platform-level, e.g. for Intel the data sizes must be
+equal to or larger than 16 bytes.
diff --git a/Documentation/driver-api/soundwire/bra_cadence.rst b/Documentation/driver-api/soundwire/bra_cadence.rst
new file mode 100644
index 000000000..4560752e8
--- /dev/null
+++ b/Documentation/driver-api/soundwire/bra_cadence.rst
@@ -0,0 +1,66 @@
+Cadence IP BRA support
+----------------------
+
+Format requirements
+~~~~~~~~~~~~~~~~~~~
+
+The Cadence IP relies on PDI0 for TX and PDI1 for RX. The data needs
+to be formatted with the following conventions:
+
+  (1) all Data is stored in bits 15..0 of the 32-bit PDI FIFOs.
+
+  (2) the start of packet is BIT(31).
+
+  (3) the end of packet is BIT(30).
+
+  (4) A packet ID is stored in bits 19..16. This packet ID is
+      determined by software and is typically a rolling counter.
+
+  (5) Padding shall be inserted as needed so that the Header CRC,
+      Header response, Footer CRC, Footer response are always in
+      Byte0. Padding is inserted by software for writes, and on reads
+      software shall discard the padding added by the hardware.
+
+Example format
+~~~~~~~~~~~~~~
+
+The following table represents the sequence provided to PDI0 for a
+write command followed by a read command.
+
+::
+
+	+---+---+--------+---------------+---------------+
+	+ 1 | 0 | ID = 0 |  WR HDR[1]    |  WR HDR[0]    |
+	+   |   |        |  WR HDR[3]    |  WR HDR[2]    |
+	+   |   |        |  WR HDR[5]    |  WR HDR[4]    |
+	+   |   |        |  pad          |  WR HDR CRC   |
+	+   |   |        |  WR Data[1]   |  WR Data[0]   |
+	+   |   |        |  WR Data[3]   |  WR Data[2]   |
+	+   |   |        |  WR Data[n-2] |  WR Data[n-3] |
+	+   |   |        |  pad          |  WR Data[n-1] |
+	+ 0 | 1 |        |  pad          |  WR Data CRC  |
+	+---+---+--------+---------------+---------------+
+	+ 1 | 0 | ID = 1 |  RD HDR[1]    |  RD HDR[0]    |
+	+   |   |        |  RD HDR[3]    |  RD HDR[2]    |
+	+   |   |        |  RD HDR[5]    |  RD HDR[4]    |
+	+ 0 | 1 |        |  pad          |  RD HDR CRC   |
+	+---+---+--------+---------------+---------------+
+
+
+The table below represents the data received on PDI1 for the same
+write command followed by a read command.
+
+::
+
+	+---+---+--------+---------------+---------------+
+	+ 1 | 0 | ID = 0 |  pad          |  WR Hdr Rsp   |
+	+ 0 | 1 |        |  pad          |  WR Ftr Rsp   |
+	+---+---+--------+---------------+---------------+
+	+ 1 | 0 | ID = 0 |  pad          |  Rd Hdr Rsp   |
+	+   |   |        |  RD Data[1]   |  RD Data[0]   |
+	+   |   |        |  RD Data[3]   |  RD Data[2]   |
+	+   |   |        |  RD HDR[n-2]  |  RD Data[n-3] |
+	+   |   |        |  pad          |  RD Data[n-1] |
+	+   |   |        |  pad          |  RD Data CRC  |
+	+ 0 | 1 |        |  pad          |  RD Ftr Rsp   |
+	+---+---+--------+---------------+---------------+
diff --git a/Documentation/driver-api/soundwire/error_handling.rst b/Documentation/driver-api/soundwire/error_handling.rst
new file mode 100644
index 000000000..aa3a0a23a
--- /dev/null
+++ b/Documentation/driver-api/soundwire/error_handling.rst
@@ -0,0 +1,65 @@
+========================
+SoundWire Error Handling
+========================
+
+The SoundWire PHY was designed with care and errors on the bus are going to
+be very unlikely, and if they happen it should be limited to single bit
+errors. Examples of this design can be found in the synchronization
+mechanism (sync loss after two errors) and short CRCs used for the Bulk
+Register Access.
+
+The errors can be detected with multiple mechanisms:
+
+1. Bus clash or parity errors: This mechanism relies on low-level detectors
+   that are independent of the payload and usages, and they cover both control
+   and audio data. The current implementation only logs such errors.
+   Improvements could be invalidating an entire programming sequence and
+   restarting from a known position. In the case of such errors outside of a
+   control/command sequence, there is no concealment or recovery for audio
+   data enabled by the SoundWire protocol, the location of the error will also
+   impact its audibility (most-significant bits will be more impacted in PCM),
+   and after a number of such errors are detected the bus might be reset. Note
+   that bus clashes due to programming errors (two streams using the same bit
+   slots) or electrical issues during the transmit/receive transition cannot
+   be distinguished, although a recurring bus clash when audio is enabled is a
+   indication of a bus allocation issue. The interrupt mechanism can also help
+   identify Slaves which detected a Bus Clash or a Parity Error, but they may
+   not be responsible for the errors so resetting them individually is not a
+   viable recovery strategy.
+
+2. Command status: Each command is associated with a status, which only
+   covers transmission of the data between devices. The ACK status indicates
+   that the command was received and will be executed by the end of the
+   current frame. A NAK indicates that the command was in error and will not
+   be applied. In case of a bad programming (command sent to non-existent
+   Slave or to a non-implemented register) or electrical issue, no response
+   signals the command was ignored. Some Master implementations allow for a
+   command to be retransmitted several times.  If the retransmission fails,
+   backtracking and restarting the entire programming sequence might be a
+   solution. Alternatively some implementations might directly issue a bus
+   reset and re-enumerate all devices.
+
+3. Timeouts: In a number of cases such as ChannelPrepare or
+   ClockStopPrepare, the bus driver is supposed to poll a register field until
+   it transitions to a NotFinished value of zero. The MIPI SoundWire spec 1.1
+   does not define timeouts but the MIPI SoundWire DisCo document adds
+   recommendation on timeouts. If such configurations do not complete, the
+   driver will return a -ETIMEOUT. Such timeouts are symptoms of a faulty
+   Slave device and are likely impossible to recover from.
+
+Errors during global reconfiguration sequences are extremely difficult to
+handle:
+
+1. BankSwitch: An error during the last command issuing a BankSwitch is
+   difficult to backtrack from. Retransmitting the Bank Switch command may be
+   possible in a single segment setup, but this can lead to synchronization
+   problems when enabling multiple bus segments (a command with side effects
+   such as frame reconfiguration would be handled at different times). A global
+   hard-reset might be the best solution.
+
+Note that SoundWire does not provide a mechanism to detect illegal values
+written in valid registers. In a number of cases the standard even mentions
+that the Slave might behave in implementation-defined ways. The bus
+implementation does not provide a recovery mechanism for such errors, Slave
+or Master driver implementers are responsible for writing valid values in
+valid registers and implement additional range checking if needed.
diff --git a/Documentation/driver-api/soundwire/index.rst b/Documentation/driver-api/soundwire/index.rst
new file mode 100644
index 000000000..f7abf4a95
--- /dev/null
+++ b/Documentation/driver-api/soundwire/index.rst
@@ -0,0 +1,13 @@
+=======================
+SoundWire Documentation
+=======================
+
+.. toctree::
+   :maxdepth: 1
+
+   summary
+   stream
+   error_handling
+   locking
+   bra
+   bra_cadence
diff --git a/Documentation/driver-api/soundwire/locking.rst b/Documentation/driver-api/soundwire/locking.rst
new file mode 100644
index 000000000..3a7ffb3d8
--- /dev/null
+++ b/Documentation/driver-api/soundwire/locking.rst
@@ -0,0 +1,108 @@
+=================
+SoundWire Locking
+=================
+
+This document explains locking mechanism of the SoundWire Bus. Bus uses
+following locks in order to avoid race conditions in Bus operations on
+shared resources.
+
+  - Bus lock
+
+  - Message lock
+
+Bus lock
+========
+
+SoundWire Bus lock is a mutex and is part of Bus data structure
+(sdw_bus) which is used for every Bus instance. This lock is used to
+serialize each of the following operations(s) within SoundWire Bus instance.
+
+  - Addition and removal of Slave(s), changing Slave status.
+
+  - Prepare, Enable, Disable and De-prepare stream operations.
+
+  - Access of Stream data structure.
+
+Message lock
+============
+
+SoundWire message transfer lock. This mutex is part of
+Bus data structure (sdw_bus). This lock is used to serialize the message
+transfers (read/write) within a SoundWire Bus instance.
+
+Below examples show how locks are acquired.
+
+Example 1
+---------
+
+Message transfer.
+
+  1. For every message transfer
+
+     a. Acquire Message lock.
+
+     b. Transfer message (Read/Write) to Slave1 or broadcast message on
+        Bus in case of bank switch.
+
+     c. Release Message lock
+
+     ::
+
+	+----------+                    +---------+
+	|          |                    |         |
+	|   Bus    |                    | Master  |
+	|          |                    | Driver  |
+	|          |                    |         |
+	+----+-----+                    +----+----+
+	     |                               |
+	     |     bus->ops->xfer_msg()      |
+	     <-------------------------------+   a. Acquire Message lock
+	     |                               |   b. Transfer message
+	     |                               |
+	     +------------------------------->   c. Release Message lock
+	     |    return success/error       |   d. Return success/error
+	     |                               |
+	     +                               +
+
+Example 2
+---------
+
+Prepare operation.
+
+  1. Acquire lock for Bus instance associated with Master 1.
+
+  2. For every message transfer in Prepare operation
+
+     a. Acquire Message lock.
+
+     b. Transfer message (Read/Write) to Slave1 or broadcast message on
+        Bus in case of bank switch.
+
+     c. Release Message lock.
+
+  3. Release lock for Bus instance associated with Master 1 ::
+
+	+----------+                    +---------+
+	|          |                    |         |
+	|   Bus    |                    | Master  |
+	|          |                    | Driver  |
+	|          |                    |         |
+	+----+-----+                    +----+----+
+	     |                               |
+	     |    sdw_prepare_stream()       |
+	     <-------------------------------+   1. Acquire bus lock
+	     |                               |   2. Perform stream prepare
+	     |                               |
+	     |                               |
+	     |     bus->ops->xfer_msg()      |
+	     <-------------------------------+   a. Acquire Message lock
+	     |                               |   b. Transfer message
+	     |                               |
+	     +------------------------------->   c. Release Message lock
+	     |    return success/error       |   d. Return success/error
+	     |                               |
+	     |                               |
+	     |    return success/error       |   3. Release bus lock
+	     +------------------------------->   4. Return success/error
+	     |                               |
+	     +                               +
diff --git a/Documentation/driver-api/soundwire/stream.rst b/Documentation/driver-api/soundwire/stream.rst
new file mode 100644
index 000000000..d66201299
--- /dev/null
+++ b/Documentation/driver-api/soundwire/stream.rst
@@ -0,0 +1,527 @@
+=========================
+Audio Stream in SoundWire
+=========================
+
+An audio stream is a logical or virtual connection created between
+
+  (1) System memory buffer(s) and Codec(s)
+
+  (2) DSP memory buffer(s) and Codec(s)
+
+  (3) FIFO(s) and Codec(s)
+
+  (4) Codec(s) and Codec(s)
+
+which is typically driven by a DMA(s) channel through the data link. An
+audio stream contains one or more channels of data. All channels within
+stream must have same sample rate and same sample size.
+
+Assume a stream with two channels (Left & Right) is opened using SoundWire
+interface. Below are some ways a stream can be represented in SoundWire.
+
+Stream Sample in memory (System memory, DSP memory or FIFOs) ::
+
+	-------------------------
+	| L | R | L | R | L | R |
+	-------------------------
+
+Example 1: Stereo Stream with L and R channels is rendered from Master to
+Slave. Both Master and Slave is using single port. ::
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +----------------------------------+     Slave     |
+	|   Interface   |                                  |   Interface   |
+	|               |                                  |       1       |
+	|               |                     Data Signal  |               |
+	|    L  +  R    +----------------------------------+    L  +  R    |
+	|     (Data)    |     Data Direction               |     (Data)    |
+	+---------------+  +----------------------->       +---------------+
+
+
+Example 2: Stereo Stream with L and R channels is captured from Slave to
+Master. Both Master and Slave is using single port. ::
+
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +----------------------------------+     Slave     |
+	|   Interface   |                                  |   Interface   |
+	|               |                                  |       1       |
+	|               |                     Data Signal  |               |
+	|    L  +  R    +----------------------------------+    L  +  R    |
+	|     (Data)    |     Data Direction               |     (Data)    |
+	+---------------+  <-----------------------+       +---------------+
+
+
+Example 3: Stereo Stream with L and R channels is rendered by Master. Each
+of the L and R channel is received by two different Slaves. Master and both
+Slaves are using single port. ::
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +---------+------------------------+     Slave     |
+	|   Interface   |         |                        |   Interface   |
+	|               |         |                        |       1       |
+	|               |         |           Data Signal  |               |
+	|    L  +  R    +---+------------------------------+       L       |
+	|     (Data)    |   |     |    Data Direction      |     (Data)    |
+	+---------------+   |     |   +------------->      +---------------+
+	                    |     |
+	                    |     |
+	                    |     |                        +---------------+
+	                    |     +----------------------> |     Slave     |
+	                    |                              |   Interface   |
+	                    |                              |       2       |
+	                    |                              |               |
+	                    +----------------------------> |       R       |
+	                                                   |     (Data)    |
+	                                                   +---------------+
+
+Example 4: Stereo Stream with L and R channels is rendered by
+Master. Both of the L and R channels are received by two different
+Slaves. Master and both Slaves are using single port handling
+L+R. Each Slave device processes the L + R data locally, typically
+based on static configuration or dynamic orientation, and may drive
+one or more speakers. ::
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +---------+------------------------+     Slave     |
+	|   Interface   |         |                        |   Interface   |
+	|               |         |                        |       1       |
+	|               |         |           Data Signal  |               |
+	|    L  +  R    +---+------------------------------+     L + R     |
+	|     (Data)    |   |     |    Data Direction      |     (Data)    |
+	+---------------+   |     |   +------------->      +---------------+
+	                    |     |
+	                    |     |
+	                    |     |                        +---------------+
+	                    |     +----------------------> |     Slave     |
+	                    |                              |   Interface   |
+	                    |                              |       2       |
+	                    |                              |               |
+	                    +----------------------------> |     L + R     |
+	                                                   |     (Data)    |
+	                                                   +---------------+
+
+Example 5: Stereo Stream with L and R channel is rendered by two different
+Ports of the Master and is received by only single Port of the Slave
+interface. ::
+
+	+--------------------+
+	|                    |
+	|     +--------------+                             +----------------+
+	|     |             ||                             |                |
+	|     |  Data Port  ||  L Channel                  |                |
+	|     |      1      |------------+                 |                |
+	|     |  L Channel  ||           |                 +-----+----+     |
+	|     |   (Data)    ||           |   L + R Channel ||    Data |     |
+	| Master  +----------+           | +---+---------> ||    Port |     |
+	| Interface          |           |                 ||     1   |     |
+	|     +--------------+           |                 ||         |     |
+	|     |             ||           |                 +----------+     |
+	|     |  Data Port  |------------+                 |                |
+	|     |      2      ||  R Channel                  |     Slave      |
+	|     |  R Channel  ||                             |   Interface    |
+	|     |   (Data)    ||                             |       1        |
+	|     +--------------+         Clock Signal        |     L  +  R    |
+	|                    +---------------------------> |      (Data)    |
+	+--------------------+                             |                |
+							   +----------------+
+
+Example 6: Stereo Stream with L and R channel is rendered by 2 Masters, each
+rendering one channel, and is received by two different Slaves, each
+receiving one channel. Both Masters and both Slaves are using single port. ::
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +----------------------------------+     Slave     |
+	|   Interface   |                                  |   Interface   |
+	|       1       |                                  |       1       |
+	|               |                     Data Signal  |               |
+	|       L       +----------------------------------+       L       |
+	|     (Data)    |     Data Direction               |     (Data)    |
+	+---------------+  +----------------------->       +---------------+
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +----------------------------------+     Slave     |
+	|   Interface   |                                  |   Interface   |
+	|       2       |                                  |       2       |
+	|               |                     Data Signal  |               |
+	|       R       +----------------------------------+       R       |
+	|     (Data)    |     Data Direction               |     (Data)    |
+	+---------------+  +----------------------->       +---------------+
+
+Example 7: Stereo Stream with L and R channel is rendered by 2
+Masters, each rendering both channels. Each Slave receives L + R. This
+is the same application as Example 4 but with Slaves placed on
+separate links. ::
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +----------------------------------+     Slave     |
+	|   Interface   |                                  |   Interface   |
+	|       1       |                                  |       1       |
+	|               |                     Data Signal  |               |
+	|     L + R     +----------------------------------+     L + R     |
+	|     (Data)    |     Data Direction               |     (Data)    |
+	+---------------+  +----------------------->       +---------------+
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +----------------------------------+     Slave     |
+	|   Interface   |                                  |   Interface   |
+	|       2       |                                  |       2       |
+	|               |                     Data Signal  |               |
+	|     L + R     +----------------------------------+     L + R     |
+	|     (Data)    |     Data Direction               |     (Data)    |
+	+---------------+  +----------------------->       +---------------+
+
+Example 8: 4-channel Stream is rendered by 2 Masters, each rendering a
+2 channels. Each Slave receives 2 channels. ::
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +----------------------------------+     Slave     |
+	|   Interface   |                                  |   Interface   |
+	|       1       |                                  |       1       |
+	|               |                     Data Signal  |               |
+	|    L1 + R1    +----------------------------------+    L1 + R1    |
+	|     (Data)    |     Data Direction               |     (Data)    |
+	+---------------+  +----------------------->       +---------------+
+
+	+---------------+                    Clock Signal  +---------------+
+	|    Master     +----------------------------------+     Slave     |
+	|   Interface   |                                  |   Interface   |
+	|       2       |                                  |       2       |
+	|               |                     Data Signal  |               |
+	|     L2 + R2   +----------------------------------+    L2 + R2    |
+	|     (Data)    |     Data Direction               |     (Data)    |
+	+---------------+  +----------------------->       +---------------+
+
+Note1: In multi-link cases like above, to lock, one would acquire a global
+lock and then go on locking bus instances. But, in this case the caller
+framework(ASoC DPCM) guarantees that stream operations on a card are
+always serialized. So, there is no race condition and hence no need for
+global lock.
+
+Note2: A Slave device may be configured to receive all channels
+transmitted on a link for a given Stream (Example 4) or just a subset
+of the data (Example 3). The configuration of the Slave device is not
+handled by a SoundWire subsystem API, but instead by the
+snd_soc_dai_set_tdm_slot() API. The platform or machine driver will
+typically configure which of the slots are used. For Example 4, the
+same slots would be used by all Devices, while for Example 3 the Slave
+Device1 would use e.g. Slot 0 and Slave device2 slot 1.
+
+Note3: Multiple Sink ports can extract the same information for the
+same bitSlots in the SoundWire frame, however multiple Source ports
+shall be configured with different bitSlot configurations. This is the
+same limitation as with I2S/PCM TDM usages.
+
+SoundWire Stream Management flow
+================================
+
+Stream definitions
+------------------
+
+  (1) Current stream: This is classified as the stream on which operation has
+      to be performed like prepare, enable, disable, de-prepare etc.
+
+  (2) Active stream: This is classified as the stream which is already active
+      on Bus other than current stream. There can be multiple active streams
+      on the Bus.
+
+SoundWire Bus manages stream operations for each stream getting
+rendered/captured on the SoundWire Bus. This section explains Bus operations
+done for each of the stream allocated/released on Bus. Following are the
+stream states maintained by the Bus for each of the audio stream.
+
+
+SoundWire stream states
+-----------------------
+
+Below shows the SoundWire stream states and state transition diagram. ::
+
+	+-----------+     +------------+     +----------+     +----------+
+	| ALLOCATED +---->| CONFIGURED +---->| PREPARED +---->| ENABLED  |
+	|   STATE   |     |    STATE   |     |  STATE   |     |  STATE   |
+	+-----------+     +------------+     +---+--+---+     +----+-----+
+	                                         ^  ^              ^
+				                 |  |              |
+				               __|  |___________   |
+				              |                 |  |
+	                                      v                 |  v
+	         +----------+           +-----+------+        +-+--+-----+
+	         | RELEASED |<----------+ DEPREPARED |<-------+ DISABLED |
+	         |  STATE   |           |   STATE    |        |  STATE   |
+	         +----------+           +------------+        +----------+
+
+NOTE: State transitions between ``SDW_STREAM_ENABLED`` and
+``SDW_STREAM_DISABLED`` are only relevant when then INFO_PAUSE flag is
+supported at the ALSA/ASoC level. Likewise the transition between
+``SDW_DISABLED_STATE`` and ``SDW_PREPARED_STATE`` depends on the
+INFO_RESUME flag.
+
+NOTE2: The framework implements basic state transition checks, but
+does not e.g. check if a transition from DISABLED to ENABLED is valid
+on a specific platform. Such tests need to be added at the ALSA/ASoC
+level.
+
+Stream State Operations
+-----------------------
+
+Below section explains the operations done by the Bus on Master(s) and
+Slave(s) as part of stream state transitions.
+
+SDW_STREAM_ALLOCATED
+~~~~~~~~~~~~~~~~~~~~
+
+Allocation state for stream. This is the entry state
+of the stream. Operations performed before entering in this state:
+
+  (1) A stream runtime is allocated for the stream. This stream
+      runtime is used as a reference for all the operations performed
+      on the stream.
+
+  (2) The resources required for holding stream runtime information are
+      allocated and initialized. This holds all stream related information
+      such as stream type (PCM/PDM) and parameters, Master and Slave
+      interface associated with the stream, stream state etc.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_ALLOCATED``.
+
+Bus implements below API for allocate a stream which needs to be called once
+per stream. From ASoC DPCM framework, this stream state maybe linked to
+.startup() operation.
+
+.. code-block:: c
+
+  int sdw_alloc_stream(char * stream_name, enum sdw_stream_type type);
+
+The SoundWire core provides a sdw_startup_stream() helper function,
+typically called during a dailink .startup() callback, which performs
+stream allocation and sets the stream pointer for all DAIs
+connected to a stream.
+
+SDW_STREAM_CONFIGURED
+~~~~~~~~~~~~~~~~~~~~~
+
+Configuration state of stream. Operations performed before entering in
+this state:
+
+  (1) The resources allocated for stream information in SDW_STREAM_ALLOCATED
+      state are updated here. This includes stream parameters, Master(s)
+      and Slave(s) runtime information associated with current stream.
+
+  (2) All the Master(s) and Slave(s) associated with current stream provide
+      the port information to Bus which includes port numbers allocated by
+      Master(s) and Slave(s) for current stream and their channel mask.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_CONFIGURED``.
+
+Bus implements below APIs for CONFIG state which needs to be called by
+the respective Master(s) and Slave(s) associated with stream. These APIs can
+only be invoked once by respective Master(s) and Slave(s). From ASoC DPCM
+framework, this stream state is linked to .hw_params() operation.
+
+.. code-block:: c
+
+  int sdw_stream_add_master(struct sdw_bus * bus,
+		struct sdw_stream_config * stream_config,
+		const struct sdw_ports_config * ports_config,
+		struct sdw_stream_runtime * stream);
+
+  int sdw_stream_add_slave(struct sdw_slave * slave,
+		struct sdw_stream_config * stream_config,
+		const struct sdw_ports_config * ports_config,
+		struct sdw_stream_runtime * stream);
+
+
+SDW_STREAM_PREPARED
+~~~~~~~~~~~~~~~~~~~
+
+Prepare state of stream. Operations performed before entering in this state:
+
+  (0) Steps 1 and 2 are omitted in the case of a resume operation,
+      where the bus bandwidth is known.
+
+  (1) Bus parameters such as bandwidth, frame shape, clock frequency,
+      are computed based on current stream as well as already active
+      stream(s) on Bus. Re-computation is required to accommodate current
+      stream on the Bus.
+
+  (2) Transport and port parameters of all Master(s) and Slave(s) port(s) are
+      computed for the current as well as already active stream based on frame
+      shape and clock frequency computed in step 1.
+
+  (3) Computed Bus and transport parameters are programmed in Master(s) and
+      Slave(s) registers. The banked registers programming is done on the
+      alternate bank (bank currently unused). Port(s) are enabled for the
+      already active stream(s) on the alternate bank (bank currently unused).
+      This is done in order to not disrupt already active stream(s).
+
+  (4) Once all the values are programmed, Bus initiates switch to alternate
+      bank where all new values programmed gets into effect.
+
+  (5) Ports of Master(s) and Slave(s) for current stream are prepared by
+      programming PrepareCtrl register.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_PREPARED``.
+
+Bus implements below API for PREPARE state which needs to be called
+once per stream. From ASoC DPCM framework, this stream state is linked
+to .prepare() operation. Since the .trigger() operations may not
+follow the .prepare(), a direct transition from
+``SDW_STREAM_PREPARED`` to ``SDW_STREAM_DEPREPARED`` is allowed.
+
+.. code-block:: c
+
+  int sdw_prepare_stream(struct sdw_stream_runtime * stream);
+
+
+SDW_STREAM_ENABLED
+~~~~~~~~~~~~~~~~~~
+
+Enable state of stream. The data port(s) are enabled upon entering this state.
+Operations performed before entering in this state:
+
+  (1) All the values computed in SDW_STREAM_PREPARED state are programmed
+      in alternate bank (bank currently unused). It includes programming of
+      already active stream(s) as well.
+
+  (2) All the Master(s) and Slave(s) port(s) for the current stream are
+      enabled on alternate bank (bank currently unused) by programming
+      ChannelEn register.
+
+  (3) Once all the values are programmed, Bus initiates switch to alternate
+      bank where all new values programmed gets into effect and port(s)
+      associated with current stream are enabled.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_ENABLED``.
+
+Bus implements below API for ENABLE state which needs to be called once per
+stream. From ASoC DPCM framework, this stream state is linked to
+.trigger() start operation.
+
+.. code-block:: c
+
+  int sdw_enable_stream(struct sdw_stream_runtime * stream);
+
+SDW_STREAM_DISABLED
+~~~~~~~~~~~~~~~~~~~
+
+Disable state of stream. The data port(s) are disabled upon exiting this state.
+Operations performed before entering in this state:
+
+  (1) All the Master(s) and Slave(s) port(s) for the current stream are
+      disabled on alternate bank (bank currently unused) by programming
+      ChannelEn register.
+
+  (2) All the current configuration of Bus and active stream(s) are programmed
+      into alternate bank (bank currently unused).
+
+  (3) Once all the values are programmed, Bus initiates switch to alternate
+      bank where all new values programmed gets into effect and port(s) associated
+      with current stream are disabled.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_DISABLED``.
+
+Bus implements below API for DISABLED state which needs to be called once
+per stream. From ASoC DPCM framework, this stream state is linked to
+.trigger() stop operation.
+
+When the INFO_PAUSE flag is supported, a direct transition to
+``SDW_STREAM_ENABLED`` is allowed.
+
+For resume operations where ASoC will use the .prepare() callback, the
+stream can transition from ``SDW_STREAM_DISABLED`` to
+``SDW_STREAM_PREPARED``, with all required settings restored but
+without updating the bandwidth and bit allocation.
+
+.. code-block:: c
+
+  int sdw_disable_stream(struct sdw_stream_runtime * stream);
+
+
+SDW_STREAM_DEPREPARED
+~~~~~~~~~~~~~~~~~~~~~
+
+De-prepare state of stream. Operations performed before entering in this
+state:
+
+  (1) All the port(s) of Master(s) and Slave(s) for current stream are
+      de-prepared by programming PrepareCtrl register.
+
+  (2) The payload bandwidth of current stream is reduced from the total
+      bandwidth requirement of bus and new parameters calculated and
+      applied by performing bank switch etc.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_DEPREPARED``.
+
+Bus implements below API for DEPREPARED state which needs to be called
+once per stream. ALSA/ASoC do not have a concept of 'deprepare', and
+the mapping from this stream state to ALSA/ASoC operation may be
+implementation specific.
+
+When the INFO_PAUSE flag is supported, the stream state is linked to
+the .hw_free() operation - the stream is not deprepared on a
+TRIGGER_STOP.
+
+Other implementations may transition to the ``SDW_STREAM_DEPREPARED``
+state on TRIGGER_STOP, should they require a transition through the
+``SDW_STREAM_PREPARED`` state.
+
+.. code-block:: c
+
+  int sdw_deprepare_stream(struct sdw_stream_runtime * stream);
+
+
+SDW_STREAM_RELEASED
+~~~~~~~~~~~~~~~~~~~
+
+Release state of stream. Operations performed before entering in this state:
+
+  (1) Release port resources for all Master(s) and Slave(s) port(s)
+      associated with current stream.
+
+  (2) Release Master(s) and Slave(s) runtime resources associated with
+      current stream.
+
+  (3) Release stream runtime resources associated with current stream.
+
+After all above operations are successful, stream state is set to
+``SDW_STREAM_RELEASED``.
+
+Bus implements below APIs for RELEASE state which needs to be called by
+all the Master(s) and Slave(s) associated with stream. From ASoC DPCM
+framework, this stream state is linked to .hw_free() operation.
+
+.. code-block:: c
+
+  int sdw_stream_remove_master(struct sdw_bus * bus,
+		struct sdw_stream_runtime * stream);
+  int sdw_stream_remove_slave(struct sdw_slave * slave,
+		struct sdw_stream_runtime * stream);
+
+
+The .shutdown() ASoC DPCM operation calls below Bus API to release
+stream assigned as part of ALLOCATED state.
+
+In .shutdown() the data structure maintaining stream state are freed up.
+
+.. code-block:: c
+
+  void sdw_release_stream(struct sdw_stream_runtime * stream);
+
+The SoundWire core provides a sdw_shutdown_stream() helper function,
+typically called during a dailink .shutdown() callback, which clears
+the stream pointer for all DAIS connected to a stream and releases the
+memory allocated for the stream.
+
+Not Supported
+=============
+
+1. A single port with multiple channels supported cannot be used between two
+   streams or across stream. For example a port with 4 channels cannot be used
+   to handle 2 independent stereo streams even though it's possible in theory
+   in SoundWire.
diff --git a/Documentation/driver-api/soundwire/summary.rst b/Documentation/driver-api/soundwire/summary.rst
new file mode 100644
index 000000000..df7805374
--- /dev/null
+++ b/Documentation/driver-api/soundwire/summary.rst
@@ -0,0 +1,200 @@
+===========================
+SoundWire Subsystem Summary
+===========================
+
+SoundWire is a new interface ratified in 2015 by the MIPI Alliance.
+SoundWire is used for transporting data typically related to audio
+functions. SoundWire interface is optimized to integrate audio devices in
+mobile or mobile inspired systems.
+
+SoundWire is a 2-pin multi-drop interface with data and clock line. It
+facilitates development of low cost, efficient, high performance systems.
+Broad level key features of SoundWire interface include:
+
+ (1) Transporting all of payload data channels, control information, and setup
+     commands over a single two-pin interface.
+
+ (2) Lower clock frequency, and hence lower power consumption, by use of DDR
+     (Dual Data Rate) data transmission.
+
+ (3) Clock scaling and optional multiple data lanes to give wide flexibility
+     in data rate to match system requirements.
+
+ (4) Device status monitoring, including interrupt-style alerts to the Master.
+
+The SoundWire protocol supports up to eleven Slave interfaces. All the
+interfaces share the common Bus containing data and clock line. Each of the
+Slaves can support up to 14 Data Ports. 13 Data Ports are dedicated to audio
+transport. Data Port0 is dedicated to transport of Bulk control information,
+each of the audio Data Ports (1..14) can support up to 8 Channels in
+transmit or receiving mode (typically fixed direction but configurable
+direction is enabled by the specification).  Bandwidth restrictions to
+~19.2..24.576Mbits/s don't however allow for 11*13*8 channels to be
+transmitted simultaneously.
+
+Below figure shows an example of connectivity between a SoundWire Master and
+two Slave devices. ::
+
+        +---------------+                                       +---------------+
+        |               |                       Clock Signal    |               |
+        |    Master     |-------+-------------------------------|    Slave      |
+        |   Interface   |       |               Data Signal     |  Interface 1  |
+        |               |-------|-------+-----------------------|               |
+        +---------------+       |       |                       +---------------+
+                                |       |
+                                |       |
+                                |       |
+                             +--+-------+--+
+                             |             |
+                             |   Slave     |
+                             | Interface 2 |
+                             |             |
+                             +-------------+
+
+
+Terminology
+===========
+
+The MIPI SoundWire specification uses the term 'device' to refer to a Master
+or Slave interface, which of course can be confusing. In this summary and
+code we use the term interface only to refer to the hardware. We follow the
+Linux device model by mapping each Slave interface connected on the bus as a
+device managed by a specific driver. The Linux SoundWire subsystem provides
+a framework to implement a SoundWire Slave driver with an API allowing
+3rd-party vendors to enable implementation-defined functionality while
+common setup/configuration tasks are handled by the bus.
+
+Bus:
+Implements SoundWire Linux Bus which handles the SoundWire protocol.
+Programs all the MIPI-defined Slave registers. Represents a SoundWire
+Master. Multiple instances of Bus may be present in a system.
+
+Slave:
+Registers as SoundWire Slave device (Linux Device). Multiple Slave devices
+can register to a Bus instance.
+
+Slave driver:
+Driver controlling the Slave device. MIPI-specified registers are controlled
+directly by the Bus (and transmitted through the Master driver/interface).
+Any implementation-defined Slave register is controlled by Slave driver. In
+practice, it is expected that the Slave driver relies on regmap and does not
+request direct register access.
+
+Programming interfaces (SoundWire Master interface Driver)
+==========================================================
+
+SoundWire Bus supports programming interfaces for the SoundWire Master
+implementation and SoundWire Slave devices. All the code uses the "sdw"
+prefix commonly used by SoC designers and 3rd party vendors.
+
+Each of the SoundWire Master interfaces needs to be registered to the Bus.
+Bus implements API to read standard Master MIPI properties and also provides
+callback in Master ops for Master driver to implement its own functions that
+provides capabilities information. DT support is not implemented at this
+time but should be trivial to add since capabilities are enabled with the
+``device_property_`` API.
+
+The Master interface along with the Master interface capabilities are
+registered based on board file, DT or ACPI.
+
+Following is the Bus API to register the SoundWire Bus:
+
+.. code-block:: c
+
+	int sdw_bus_master_add(struct sdw_bus *bus,
+				struct device *parent,
+				struct fwnode_handle)
+	{
+		sdw_master_device_add(bus, parent, fwnode);
+
+		mutex_init(&bus->lock);
+		INIT_LIST_HEAD(&bus->slaves);
+
+		/* Check ACPI for Slave devices */
+		sdw_acpi_find_slaves(bus);
+
+		/* Check DT for Slave devices */
+		sdw_of_find_slaves(bus);
+
+		return 0;
+	}
+
+This will initialize sdw_bus object for Master device. "sdw_master_ops" and
+"sdw_master_port_ops" callback functions are provided to the Bus.
+
+"sdw_master_ops" is used by Bus to control the Bus in the hardware specific
+way. It includes Bus control functions such as sending the SoundWire
+read/write messages on Bus, setting up clock frequency & Stream
+Synchronization Point (SSP). The "sdw_master_ops" structure abstracts the
+hardware details of the Master from the Bus.
+
+"sdw_master_port_ops" is used by Bus to setup the Port parameters of the
+Master interface Port. Master interface Port register map is not defined by
+MIPI specification, so Bus calls the "sdw_master_port_ops" callback
+function to do Port operations like "Port Prepare", "Port Transport params
+set", "Port enable and disable". The implementation of the Master driver can
+then perform hardware-specific configurations.
+
+Programming interfaces (SoundWire Slave Driver)
+===============================================
+
+The MIPI specification requires each Slave interface to expose a unique
+48-bit identifier, stored in 6 read-only dev_id registers. This dev_id
+identifier contains vendor and part information, as well as a field enabling
+to differentiate between identical components. An additional class field is
+currently unused. Slave driver is written for a specific vendor and part
+identifier, Bus enumerates the Slave device based on these two ids.
+Slave device and driver match is done based on these two ids . Probe
+of the Slave driver is called by Bus on successful match between device and
+driver id. A parent/child relationship is enforced between Master and Slave
+devices (the logical representation is aligned with the physical
+connectivity).
+
+The information on Master/Slave dependencies is stored in platform data,
+board-file, ACPI or DT. The MIPI Software specification defines additional
+link_id parameters for controllers that have multiple Master interfaces. The
+dev_id registers are only unique in the scope of a link, and the link_id
+unique in the scope of a controller. Both dev_id and link_id are not
+necessarily unique at the system level but the parent/child information is
+used to avoid ambiguity.
+
+.. code-block:: c
+
+	static const struct sdw_device_id slave_id[] = {
+	        SDW_SLAVE_ENTRY(0x025d, 0x700, 0),
+	        {},
+	};
+	MODULE_DEVICE_TABLE(sdw, slave_id);
+
+	static struct sdw_driver slave_sdw_driver = {
+	        .driver = {
+	                   .name = "slave_xxx",
+	                   .pm = &slave_runtime_pm,
+	                   },
+		.probe = slave_sdw_probe,
+		.remove = slave_sdw_remove,
+		.ops = &slave_slave_ops,
+		.id_table = slave_id,
+	};
+
+
+For capabilities, Bus implements API to read standard Slave MIPI properties
+and also provides callback in Slave ops for Slave driver to implement own
+function that provides capabilities information. Bus needs to know a set of
+Slave capabilities to program Slave registers and to control the Bus
+reconfigurations.
+
+Links
+=====
+
+SoundWire MIPI specification 1.1 is available at:
+https://members.mipi.org/wg/All-Members/document/70290
+
+SoundWire MIPI DisCo (Discovery and Configuration) specification is
+available at:
+https://www.mipi.org/specifications/mipi-disco-soundwire
+
+(publicly accessible with registration or directly accessible to MIPI
+members)
+
+MIPI Alliance Manufacturer ID Page: mid.mipi.org