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

[nerdopolis <bluescreen_avenger@verizon.net>]

On Friday, September 15, 2023 4:28:20 AM EDT 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
> 
> To test it, make sure you're using the simpledrm driver, and trigger a panic:
> echo c > /proc/sysrq-trigger
> 
This seems to work pretty good! With this one, I don't need to have Weston (or another display server) running for it to work this time.
The panic reason works, which is pretty sweet.

FYI: I do get a hunk that fails to apply in simpledrm_remove in drivers/gpu/drm/tiny/simpledrm.c
Seems to be a change in a recentish commit
https://github.com/torvalds/linux/commit/84e6da7ad5537826343636b846530ec2167d4a19

Thanks!
> 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
>