Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 145 insertions, 0 deletions

diff --git a/Documentation/driver-api/media/tx-rx.rst b/Documentation/driver-api/media/tx-rx.rst
new file mode 100644
index 000000000..7df240781
--- /dev/null
+++ b/Documentation/driver-api/media/tx-rx.rst
@@ -0,0 +1,145 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _transmitter-receiver:
+
+Pixel data transmitter and receiver drivers
+===========================================
+
+V4L2 supports various devices that transmit and receive pixel data. Examples of
+these devices include a camera sensor, a TV tuner and a parallel, a BT.656 or a
+CSI-2 receiver in an SoC.
+
+Bus types
+---------
+
+The following buses are the most common. This section discusses these two only.
+
+MIPI CSI-2
+^^^^^^^^^^
+
+CSI-2 is a data bus intended for transferring images from cameras to
+the host SoC. It is defined by the `MIPI alliance`_.
+
+.. _`MIPI alliance`: https://www.mipi.org/
+
+Parallel and BT.656
+^^^^^^^^^^^^^^^^^^^
+
+The parallel and `BT.656`_ buses transport one bit of data on each clock cycle
+per data line. The parallel bus uses synchronisation and other additional
+signals whereas BT.656 embeds synchronisation.
+
+.. _`BT.656`: https://en.wikipedia.org/wiki/ITU-R_BT.656
+
+Transmitter drivers
+-------------------
+
+Transmitter drivers generally need to provide the receiver drivers with the
+configuration of the transmitter. What is required depends on the type of the
+bus. These are common for both buses.
+
+Media bus pixel code
+^^^^^^^^^^^^^^^^^^^^
+
+See :ref:`v4l2-mbus-pixelcode`.
+
+Link frequency
+^^^^^^^^^^^^^^
+
+The :ref:`V4L2_CID_LINK_FREQ <v4l2-cid-link-freq>` control is used to tell the
+receiver the frequency of the bus (i.e. it is not the same as the symbol rate).
+
+Drivers that do not have user-configurable link frequency should report it
+through the ``.get_mbus_config()`` subdev pad operation, in the ``link_freq``
+field of struct v4l2_mbus_config, instead of through controls.
+
+Receiver drivers should use :c:func:`v4l2_get_link_freq` helper to obtain the
+link frequency from the transmitter sub-device.
+
+``.enable_streams()`` and ``.disable_streams()`` callbacks
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The struct v4l2_subdev_pad_ops->enable_streams() and struct
+v4l2_subdev_pad_ops->disable_streams() callbacks are used by the receiver driver
+to control the transmitter driver's streaming state. These callbacks may not be
+called directly, but by using ``v4l2_subdev_enable_streams()`` and
+``v4l2_subdev_disable_streams()``.
+
+Stopping the transmitter
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+A transmitter stops sending the stream of images as a result of
+calling the ``.disable_streams()`` callback. Some transmitters may stop the
+stream at a frame boundary whereas others stop immediately,
+effectively leaving the current frame unfinished. The receiver driver
+should not make assumptions either way, but function properly in both
+cases.
+
+CSI-2 transmitter drivers
+-------------------------
+
+Pixel rate
+^^^^^^^^^^
+
+The pixel rate on the bus is calculated as follows::
+
+	pixel_rate = link_freq * 2 * nr_of_lanes * 16 / k / bits_per_sample
+
+where
+
+.. list-table:: variables in pixel rate calculation
+   :header-rows: 1
+
+   * - variable or constant
+     - description
+   * - link_freq
+     - The value of the :ref:`V4L2_CID_LINK_FREQ <v4l2-cid-link-freq>` integer64
+       menu item.
+   * - nr_of_lanes
+     - Number of data lanes used on the CSI-2 link.
+   * - 2
+     - Data is transferred on both rising and falling edge of the signal.
+   * - bits_per_sample
+     - Number of bits per sample.
+   * - k
+     - 16 for D-PHY and 7 for C-PHY.
+
+Information on whether D-PHY or C-PHY is used, and the value of ``nr_of_lanes``, can be obtained from the OF endpoint configuration.
+
+.. note::
+
+	The pixel rate calculated this way is **not** the same thing as the
+	pixel rate on the camera sensor's pixel array which is indicated by the
+	:ref:`V4L2_CID_PIXEL_RATE <v4l2-cid-pixel-rate>` control.
+
+LP-11 and LP-111 states
+^^^^^^^^^^^^^^^^^^^^^^^
+
+As part of transitioning to high speed mode, a CSI-2 transmitter typically
+briefly sets the bus to LP-11 or LP-111 state, depending on the PHY. This period
+may be as short as 100 µs, during which the receiver observes this state and
+proceeds its own part of high speed mode transition.
+
+Most receivers are capable of autonomously handling this once the software has
+configured them to do so, but there are receivers which require software
+involvement in observing LP-11 or LP-111 state. 100 µs is a brief period to hit
+in software, especially when there is no interrupt telling something is
+happening.
+
+One way to address this is to configure the transmitter side explicitly to LP-11
+or LP-111 state, which requires support from the transmitter hardware. This is
+not universally available. Many devices return to this state once streaming is
+stopped while the state after power-on is LP-00 or LP-000.
+
+The ``.pre_streamon()`` callback may be used to prepare a transmitter for
+transitioning to streaming state, but not yet start streaming. Similarly, the
+``.post_streamoff()`` callback is used to undo what was done by the
+``.pre_streamon()`` callback. The caller of ``.pre_streamon()`` is thus required
+to call ``.post_streamoff()`` for each successful call of ``.pre_streamon()``.
+
+In the context of CSI-2, the ``.pre_streamon()`` callback is used to transition
+the transmitter to the LP-11 or LP-111 state. This also requires powering on the
+device, so this should be only done when it is needed.
+
+Receiver drivers that do not need explicit LP-11 or LP-111 state setup are
+waived from calling the two callbacks.