[RFC][PATCH 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 the drm_client API.
This implementation with the drm client API, allocates new framebuffers, and looks a bit too complex to run in a panic handler.
Maybe we should add an API to "steal" the current framebuffer instead, because in a panic handler user-space is already stopped.

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

There is one thing I don't know how to do, is to unregister the drm_panic when the graphic driver is unloaded.
drm_client_register() says it will automatically unregister on driver unload. But then I don't know how to remove it from my linked list, and free the drm_client_dev struct.

This is a first draft, so let me know what do you think about it.

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      | 286 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/tiny/simpledrm.c |   2 +
 include/drm/drm_panic.h          |  26 +++
 6 files changed, 329 insertions(+)
 create mode 100644 drivers/gpu/drm/drm_panic.c
 create mode 100644 include/drm/drm_panic.h


base-commit: 6995e2de6891c724bfeb2db33d7b87775f913ad1
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2.41.0