Merge tag 'i3c/for-7.3' of git://git.kernel.org/pub/scm/linux/kernel/git/i3c/linuxgrafted

Pull I3C updates from Alexandre Belloni:
 "A new driver this cycle, for the AMD AXI I3C controller.

  There are also new features such as IBI wakeup support, SETAASA device
  discovery and ACPI support for the the DAA methods, meaning we can now
  communicate with the SPD devices on DDR5 modules.

  New driver:
   - AMD AXI I3C master controller

  Subsystem:
   - I3C Common Command Code (CCC) handling improvements, especially
     around GET CCCs
   - SETAASA device discovery support
   - ACPI support for all existing DAA methods like SETDASA, SETNEWDA as
     well as I2C devices on I3C bus
   - IBI-based wakeup support

  Drivers:
   - dw: SETAASA support
   - mipi-i3c-hci: advertise IBI wakeup capability, AMD_PT I3C
     controller support, PIO queue management support for HCI v1.2
   - renesas: improve suspend to RAM support, add runtime PM support"

* tag 'i3c/for-7.3' of git://git.kernel.org/pub/scm/linux/kernel/git/i3c/linux: (70 commits)
  i3c: dw: reduce do_daa time if there's no client
  i3c: mipi-i3c-hci: Add support for AMD_PT I3C controller
  i3c: mipi-i3c-hci: Add PIO queue management support for HCI v1.2
  i3c: mipi-i3c-hci: Fix missing STAT_IBI_STATUS_THLD in PIO mode
  i3c: dw: rename "pclk" to "apb" to match dt-binding
  i3c: dw: make struct dw_i3c_cmd smaller
  i3c: dw: use COMMAND_PORT_TRANSFER_ARG instead of hardcoding
  i3c: renesas: Don't register devices when ENTDAA times out
  i3c: master: dw-i3c-master: fix OD timing for first broadcast
  i3c: mipi-i3c-hci: Advertise IBI wakeup capability
  i3c: mipi-i3c-hci: Factor out i3c_hci_sysdev()
  i3c: mipi-i3c-hci-pci: Propagate I3C wakeup requirements to PCI
  i3c: master: Reject IBI requests from non-IBI-capable devices
  i3c: master: Add helper to query bus wakeup requirements
  i3c: master: Report wakeup events for IBIs
  i3c: master: Support IBI-based wakeup capability
  i3c: master: Fix potential UAF in i3c_device_match()
  i3c: master: Fix potential UAF in i3c_device_uevent()
  i3c: Make dev->desc locking assumptions explicit
  i3c: master: Fix use-after-free of master->this
  ...

1 files changed, 180 insertions, 0 deletions

diff --git a/Documentation/trace/debugging.rst b/Documentation/trace/debugging.rst
new file mode 100644
index 000000000..bca1710d9
--- /dev/null
+++ b/Documentation/trace/debugging.rst
@@ -0,0 +1,180 @@
+==============================
+Using the tracer for debugging
+==============================
+
+Copyright 2024 Google LLC.
+
+:Author:   Steven Rostedt <rostedt@goodmis.org>
+:License:  The GNU Free Documentation License, Version 1.2
+          (dual licensed under the GPL v2)
+
+- Written for: 6.12
+
+Introduction
+------------
+The tracing infrastructure can be very useful for debugging the Linux
+kernel. This document is a place to add various methods of using the tracer
+for debugging.
+
+First, make sure that the tracefs file system is mounted::
+
+ $ sudo mount -t tracefs tracefs /sys/kernel/tracing
+
+
+Using trace_printk()
+--------------------
+
+trace_printk() is a very lightweight utility that can be used in any context
+inside the kernel, with the exception of "noinstr" sections. It can be used
+in normal, softirq, interrupt and even NMI context. The trace data is
+written to the tracing ring buffer in a lockless way. To make it even
+lighter weight, when possible, it will only record the pointer to the format
+string, and save the raw arguments into the buffer. The format and the
+arguments will be post processed when the ring buffer is read. This way the
+trace_printk() format conversions are not done during the hot path, where
+the trace is being recorded.
+
+trace_printk() is meant only for debugging, and should never be added into
+a subsystem of the kernel. If you need debugging traces, add trace events
+instead. If a trace_printk() is found in the kernel, the following will
+appear in the dmesg::
+
+  **********************************************************
+  **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
+  **                                                      **
+  ** trace_printk() being used. Allocating extra memory.  **
+  **                                                      **
+  ** This means that this is a DEBUG kernel and it is     **
+  ** unsafe for production use.                           **
+  **                                                      **
+  ** If you see this message and you are not debugging    **
+  ** the kernel, report this immediately to your vendor!  **
+  **                                                      **
+  **   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **
+  **********************************************************
+
+Debugging kernel crashes
+------------------------
+There is various methods of acquiring the state of the system when a kernel
+crash occurs. This could be from the oops message in printk, or one could
+use kexec/kdump. But these just show what happened at the time of the crash.
+It can be very useful in knowing what happened up to the point of the crash.
+The tracing ring buffer, by default, is a circular buffer that will
+overwrite older events with newer ones. When a crash happens, the content of
+the ring buffer will be all the events that lead up to the crash.
+
+There are several kernel command line parameters that can be used to help in
+this. The first is "ftrace_dump_on_oops". This will dump the tracing ring
+buffer when a oops occurs to the console. This can be useful if the console
+is being logged somewhere. If a serial console is used, it may be prudent to
+make sure the ring buffer is relatively small, otherwise the dumping of the
+ring buffer may take several minutes to hours to finish. Here's an example
+of the kernel command line::
+
+  ftrace_dump_on_oops trace_buf_size=50K
+
+Note, the tracing buffer is made up of per CPU buffers where each of these
+buffers is broken up into sub-buffers that are by default PAGE_SIZE. The
+above trace_buf_size option above sets each of the per CPU buffers to 50K,
+so, on a machine with 8 CPUs, that's actually 400K total.
+
+Persistent buffers across boots
+-------------------------------
+If the system memory allows it, the tracing ring buffer can be specified at
+a specific location in memory. If the location is the same across boots and
+the memory is not modified, the tracing buffer can be retrieved from the
+following boot. There's two ways to reserve memory for the use of the ring
+buffer.
+
+The more reliable way (on x86) is to reserve memory with the "memmap" kernel
+command line option and then use that memory for the trace_instance. This
+requires a bit of knowledge of the physical memory layout of the system. The
+advantage of using this method, is that the memory for the ring buffer will
+always be the same::
+
+  memmap==12M$0x284500000 trace_instance=boot_map@0x284500000:12M
+
+The memmap above reserves 12 megabytes of memory at the physical memory
+location 0x284500000. Then the trace_instance option will create a trace
+instance "boot_map" at that same location with the same amount of memory
+reserved. As the ring buffer is broke up into per CPU buffers, the 12
+megabytes will be broken up evenly between those CPUs. If you have 8 CPUs,
+each per CPU ring buffer will be 1.5 megabytes in size. Note, that also
+includes meta data, so the amount of memory actually used by the ring buffer
+will be slightly smaller.
+
+Another more generic but less robust way to allocate a ring buffer mapping
+at boot is with the "reserve_mem" option::
+
+  reserve_mem=12M:4096:trace trace_instance=boot_map@trace
+
+The reserve_mem option above will find 12 megabytes that are available at
+boot up, and align it by 4096 bytes. It will label this memory as "trace"
+that can be used by later command line options.
+
+The trace_instance option creates a "boot_map" instance and will use the
+memory reserved by reserve_mem that was labeled as "trace". This method is
+more generic but may not be as reliable. Due to KASLR, the memory reserved
+by reserve_mem may not be located at the same location. If this happens,
+then the ring buffer will not be from the previous boot and will be reset.
+
+Sometimes, by using a larger alignment, it can keep KASLR from moving things
+around in such a way that it will move the location of the reserve_mem. By
+using a larger alignment, you may find better that the buffer is more
+consistent to where it is placed::
+
+  reserve_mem=12M:0x2000000:trace trace_instance=boot_map@trace
+
+On boot up, the memory reserved for the ring buffer is validated. It will go
+through a series of tests to make sure that the ring buffer contains valid
+data. If it is, it will then set it up to be available to read from the
+instance. If it fails any of the tests, it will clear the entire ring buffer
+and initialize it as new.
+
+The layout of this mapped memory may not be consistent from kernel to
+kernel, so only the same kernel is guaranteed to work if the mapping is
+preserved. Switching to a different kernel version may find a different
+layout and mark the buffer as invalid.
+
+NB: Both the mapped address and size must be page aligned for the architecture.
+
+Using trace_printk() in the boot instance
+-----------------------------------------
+By default, the content of trace_printk() goes into the top level tracing
+instance. But this instance is never preserved across boots. To have the
+trace_printk() content, and some other internal tracing go to the preserved
+buffer (like dump stacks), either set the instance to be the trace_printk()
+destination from the kernel command line, or set it after boot up via the
+trace_printk_dest option.
+
+After boot up::
+
+  echo 1 > /sys/kernel/tracing/instances/boot_map/options/trace_printk_dest
+
+From the kernel command line::
+
+  reserve_mem=12M:4096:trace trace_instance=boot_map^traceprintk^traceoff@trace
+
+If setting it from the kernel command line, it is recommended to also
+disable tracing with the "traceoff" flag, and enable tracing after boot up.
+Otherwise the trace from the most recent boot will be mixed with the trace
+from the previous boot, and may make it confusing to read.
+
+Using a backup instance for keeping previous boot data
+------------------------------------------------------
+
+It is also possible to record trace data at system boot time by specifying
+events with the persistent ring buffer, but in this case the data before the
+reboot will be lost before it can be read. This problem can be solved by a
+backup instance. From the kernel command line::
+
+  reserve_mem=12M:4096:trace trace_instance=boot_map@trace,sched,irq trace_instance=backup=boot_map
+
+On boot up, the previous data in the "boot_map" is copied to the "backup"
+instance, and the "sched:*" and "irq:*" events for the current boot are traced
+in the "boot_map". Thus the user can read the previous boot data from the "backup"
+instance without stopping the trace.
+
+Note that this "backup" instance is readonly, and will be removed automatically
+if you clear the trace data or read out all trace data from the "trace_pipe"
+or the "trace_pipe_raw" files.