[RFC PATCH v2 0/5] drm/log: Introduce a new boot logger to draw the kmsg on the screen

[Jocelyn Falempe <jfalempe@redhat.com>]

drm_log is a simple logger that uses the drm_client API to print the kmsg boot log on the screen.
This is not a full replacement to fbcon, as it will only print the kmsg.
It will never handle user input, or a terminal because this is better done in userspace.

If you're curious on how it looks like, I've put a small demo here:
https://people.redhat.com/jfalempe/drm_log/drm_log_draft_boot_v2.mp4

Design decisions:
  * It uses the drm_client API, so it should work on all drm drivers from the start.
  * It doesn't scroll the message, that way it doesn't need to redraw the whole screen for each new message.
    It also means it doesn't have to keep drawn messages in memory, to redraw them when scrolling.
  * It uses a circular buffer so the console->write() callback is very quick, and will never stall.
  * Drawing is done asynchronously using a workqueue.
  * drm_log can only be built-in (and drm must be built-in too).
    The reason is that, if you build it as a module, then a userspace application will be more appropriate than this module.
  * When nbcon will be ready, I will use it. It should simplify this a lot, but I prefer not to depend on it yet.
 
The first patch is not for review/merge, it's a squash of my pending drm_panic series:
https://patchwork.freedesktop.org/series/135944/

The second patch, moves the drawing function from drm_panic.c, to drm_draw.c, so they can be re-used by drm_log.
The next patches are the actual drm_log implementation.

v2:
 * Use vmap_local() api, with that change, I've tested it successfully on simpledrm, virtio-gpu, amdgpu, and nouveau.
 * Stop drawing when the drm_master is taken. This avoid wasting CPU cycle if the buffer is not visible.
 * Use deferred probe. Only do the probe the first time there is a log to draw. With this, if you boot with quiet, drm_log won't do any modeset.
 * Add color support for the timestamp prefix, like what dmesg does.
 * Add build dependency on  disabling the fbdev emulation, as they are both drm_client, and there is no way to choose which one gets the focus.

Thanks and best regards,

-- 

Jocelyn

Jocelyn Falempe (5):
  [NOT FOR REVIEW] drm/panic: Squash of pending series
  drm/panic: Move drawing functions to drm_draw
  drm/log: Introduce a new boot logger to draw the kmsg on the screen
  drm/log: Do not draw if drm_master is taken
  drm/log: Color the timestamp, to improve readability

 drivers/gpu/drm/Kconfig             |   50 ++
 drivers/gpu/drm/Makefile            |    4 +
 drivers/gpu/drm/drm_crtc_internal.h |    4 +
 drivers/gpu/drm/drm_draw.c          |  216 ++++++
 drivers/gpu/drm/drm_draw.h          |   56 ++
 drivers/gpu/drm/drm_drv.c           |    5 +
 drivers/gpu/drm/drm_log.c           |  515 ++++++++++++++
 drivers/gpu/drm/drm_log.h           |   11 +
 drivers/gpu/drm/drm_panic.c         |  569 ++++++++-------
 drivers/gpu/drm/drm_panic_qr.rs     | 1003 +++++++++++++++++++++++++++
 include/drm/drm_rect.h              |   15 +
 11 files changed, 2193 insertions(+), 255 deletions(-)
 create mode 100644 drivers/gpu/drm/drm_draw.c
 create mode 100644 drivers/gpu/drm/drm_draw.h
 create mode 100644 drivers/gpu/drm/drm_log.c
 create mode 100644 drivers/gpu/drm/drm_log.h
 create mode 100644 drivers/gpu/drm/drm_panic_qr.rs


base-commit: 8befe8fa5a4e4b30787b17e078d9d7b5cb92ea19
-- 
2.46.0