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

["Noralf Trønnes" <noralf@tronnes.org>]

Hi,

On 9/15/23 10:28, Jocelyn Falempe wrote:
> 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
> 

There's a panic handling entry in Documentation/gpu/todo.rst pointing to
some work done in this area.

Noralf.

> 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