[Intel-gfx] [PATCH v2 1/3] drm: Add support for panic message output

[Michel Dänzer]

On 2019-03-12 6:15 p.m., Noralf Trønnes wrote:
> 
> 
> Den 12.03.2019 17.17, skrev Ville Syrjälä:
>> On Tue, Mar 12, 2019 at 11:47:04AM +0100, Michel Dänzer wrote:
>>> On 2019-03-11 6:42 p.m., Noralf Trønnes wrote:
>>>> This adds support for outputting kernel messages on panic().
>>>> A kernel message dumper is used to dump the log. The dumper iterates
>>>> over each DRM device and it's crtc's to find suitable framebuffers.
>>>>
>>>> All the other dumpers are run before this one except mtdoops.
>>>> Only atomic drivers are supported.
>>>>
>>>> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
>>>> ---
>>>>  [...]
>>>>
>>>> diff --git a/include/drm/drm_framebuffer.h b/include/drm/drm_framebuffer.h
>>>> index f0b34c977ec5..f3274798ecfe 100644
>>>> --- a/include/drm/drm_framebuffer.h
>>>> +++ b/include/drm/drm_framebuffer.h
>>>> @@ -94,6 +94,44 @@ struct drm_framebuffer_funcs {
>>>>  		     struct drm_file *file_priv, unsigned flags,
>>>>  		     unsigned color, struct drm_clip_rect *clips,
>>>>  		     unsigned num_clips);
>>>> +
>>>> +	/**
>>>> +	 * @panic_vmap:
>>>> +	 *
>>>> +	 * Optional callback for panic handling.
>>>> +	 *
>>>> +	 * For vmapping the selected framebuffer in a panic context. Must
>>>> +	 * be super careful about locking (only trylocking allowed).
>>>> +	 *
>>>> +	 * RETURNS:
>>>> +	 *
>>>> +	 * NULL if it didn't work out, otherwise an opaque cookie which is
>>>> +	 * passed to @panic_draw_xy. It can be anything: vmap area, structure
>>>> +	 * with more details, just a few flags, ...
>>>> +	 */
>>>> +	void *(*panic_vmap)(struct drm_framebuffer *fb);
>>>
>>> FWIW, the panic_vmap hook cannot work in general with the amdgpu/radeon
>>> drivers:
>>>
>>> Framebuffers are normally tiled, writing to them with the CPU results in
>>> garbled output.
>>>
> 
> In which case the driver needs to support the ->panic_draw_xy callback,
> or maybe it's possible to make a generic helper for tiled buffers.

I'm afraid that won't help, at least not without porting big chunks of
https://gitlab.freedesktop.org/mesa/mesa/tree/master/src/amd/addrlib
into the kernel, none of which will be used for anything else.


>>> There would need to be a mechanism for switching scanout to a linear,
>>> CPU accessible framebuffer.
>>
>> I suppose panic_vmap() could just provide a linear temp buffer
>> to the panic handler, and panic_unmap() could copy the contents
>> over to the real fb.

Copy how? Using a GPU engine?


-- 
Earthling Michel Dänzer               |              https://www.amd.com
Libre software enthusiast             |             Mesa and X developer