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

[nerdopolis]

On Monday, August 21, 2023 9:34:52 AM EDT Jocelyn Falempe wrote:
> On 13/08/2023 04:20, nerdopolis wrote:
> > On Wednesday, August 9, 2023 3:17:27 PM 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 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.
> > Hi,
> > 
> > Oh wow, that's my post. I'm sorry about the late reply, I only saw this late yesterday, and I wanted to test it first.
> > I had to edit my test QEMU script a bit to use TianoCore for virtual UEFI boot as there is no gfxmode=keep for SimpleDRM to work otherwise when specifying -kernel to qemu AFAIK
> > 
> > I tested it, and it works! That's pretty cool, although is it possible to show the message, such as "attempted to kill init"?
> 
> Thanks for taking time to test it. Yes it's possible to show the panic 
> reason, as it's a parameter in the panic callback.
> > 
> > I like the little ASCII Tux. Maybe an ASCII /!\ or [X] on the belly would make it more obvious to users that it is an error condition.
> > Especially for non-English speaking users
> 
> That's a good idea. It's also probably possible to re-use the tux boot 
> logo, but I didn't try it yet.
> 
> But currently, my priority is to see if it can get accepted, and if it 
> can work with a wide range of drivers.
> 
Alright, that makes sense. I don't have a huge variety of hardware, but I have a udl (displaylink 2) device that can be tested once ready
> > 
> > 
> > I will tweak my script a bit so I can test it more quickly in the future too.
> 
> 
> Best Regards,
> 
> > 
> > Thanks!
> >>
> >> 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
> >>
> > 
> > 
> > 
> > 
> 
> 
>