On Tue, 14 Jan 2020 12:21:43 -0500
Sean Paul [off-list ref] wrote:

From: Sean Paul <redacted>

This patch uses a ring_buffer to keep a "flight recorder" (name credit Weston)
of DRM logs for a specified set of debug categories. The user writes a
bitmask of debug categories to the "trace_mask" node and can read log
messages from the "trace" node.

These nodes currently exist in debugfs under the dri directory. I
intended on exposing all of this through tracefs originally, but the
tracefs entry points are not exposed, so there's no way to create
tracefs files from drivers at the moment. I think it would be a
worthwhile endeavour, but one requiring more time and conversation to
ensure the drm traces fit somewhere sensible.

You may want to rebase these on my tree that renames ring_buffer to
trace_buffer. For more information, read this thread:

  https://lore.kernel.org/r/20191213153553.GE20583@krava (local)

My tree is currently being tested and when it finishes contingent on no
errors found, I'll be pushing it to linux-next.

 https://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git/commit/?h=ftrace/core&id=13292494379f92f532de71b31a54018336adc589

-- Steve

Cc: Daniel Vetter <redacted>
Cc: David Airlie <airlied@gmail.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Rob Clark <redacted>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Ville Syrjälä <redacted>
Signed-off-by: Sean Paul <redacted>
Link: https://patchwork.freedesktop.org/patch/msgid/20191010204823.195540-1-sean@poorly.run #v1
Link: https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html #v2
Link: https://patchwork.freedesktop.org/patch/msgid/20191212203301.142437-1-sean@poorly.run #v3

Changes in v2:
- Went with a completely different approach:
https://lists.freedesktop.org/archives/dri-devel/2019-November/243230.html

Changes in v3:
- Changed commit message to be a bit less RFC-y
- Make class_drm_category_log an actual trace class

Changes in v4:
- Instead of [ab]using trace events and the system trace buffer, use our
  own ringbuffer
---