[RFC][PATCH v2 0/2] drm/panic: Add a drm panic handler

[Jocelyn Falempe]

This introduces a new drm panic handler, which displays a message when a panic occurs.
So when fbcon is disabled, you can still see a kernel panic.

This is one of the missing feature, when disabling VT/fbcon in the kernel:
https://www.reddit.com/r/linux/comments/10eccv9/config_vtn_in_2023/
Fbcon can be replaced by a userspace kms console, but the panic screen must be done in the kernel.

This is a proof of concept, and works only with simpledrm, using a new get_scanout_buffer() api

To test it, make sure you're using the simpledrm driver, and trigger a panic:
echo c > /proc/sysrq-trigger

v2
 * Use get_scanout_buffer() instead of the drm client API. (Thomas Zimmermann)
 * Add the panic reason to the panic message (Nerdopolis)
 * Add an exclamation mark (Nerdopolis)
 
I didn't reuse the fbdev functions yet, that would need some fbdev refactoring, because they rely on struct fb_info, and struct vc_data (for font/console). But I still plan to at least try it for v3.

A few more though:
 1) what about gpu with multiple monitor connected ?
maybe get_scanout_buffer() could return a list of scanout buffers ?
 2) I think for some GPU drivers, there might need a flush_scanout_buffer() function, that should be called after the scanout buffer has been filled ?

Best regards,

Jocelyn Falempe (2):
  drm/panic: Add a drm panic handler
  drm/simpledrm: Add drm_panic support

 drivers/gpu/drm/Kconfig          |  11 ++
 drivers/gpu/drm/Makefile         |   1 +
 drivers/gpu/drm/drm_drv.c        |   3 +
 drivers/gpu/drm/drm_panic.c      | 270 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/tiny/simpledrm.c |  17 ++
 include/drm/drm_drv.h            |  14 ++
 include/drm/drm_panic.h          |  41 +++++
 7 files changed, 357 insertions(+)
 create mode 100644 drivers/gpu/drm/drm_panic.c
 create mode 100644 include/drm/drm_panic.h


base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
-- 
2.41.0