[PATCH v4 2/4] drm/panic: Add a drm panic handler

[Jocelyn Falempe]

On 05/10/2023 10:18, Maxime Ripard wrote:
> Hi,
> 
> On Tue, Oct 03, 2023 at 04:22:45PM +0200, Jocelyn Falempe wrote:
>> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
>> index 89e2706cac56..e538c87116d3 100644
>> --- a/include/drm/drm_drv.h
>> +++ b/include/drm/drm_drv.h
>> @@ -43,6 +43,7 @@ struct dma_buf_attachment;
>>   struct drm_display_mode;
>>   struct drm_mode_create_dumb;
>>   struct drm_printer;
>> +struct drm_scanout_buffer;
>>   struct sg_table;
>>   
>>   /**
>> @@ -408,6 +409,19 @@ struct drm_driver {
>>   	 */
>>   	void (*show_fdinfo)(struct drm_printer *p, struct drm_file *f);
>>   
>> +	/**
>> +	 * @get_scanout_buffer:
>> +	 *
>> +	 * Get the current scanout buffer, to display a panic message with drm_panic.
>> +	 * It is called from a panic callback, and must follow its restrictions.
>> +	 *
>> +	 * Returns:
>> +	 *
>> +	 * Zero on success, negative errno on failure.
>> +	 */
>> +	int (*get_scanout_buffer)(struct drm_device *dev,
>> +				  struct drm_scanout_buffer *sb);
>> +
> 
> What is the format of that buffer? What is supposed to happen if the
> planes / CRTC are setup in a way that is incompatible with the buffer
> format?

Currently, it only supports linear format, either in system memory, or 
iomem.
But really what is needed is the screen size, and a way to write pixels 
to it.
For more complex GPU, I don't know if it's easier to reprogram the GPU 
to linear format, or to add a simple "tiled" support to drm_panic.
What would you propose as a panic interface to handle those complex format ?

Sometime it's also just not possible to write pixels to the screen, like 
if the panic occurs in the middle of suspend/resume, or during a 
mode-setting, and the hardware state is broken. In this case it's ok to 
return an error, and nothing will get displayed.

Best regards,

--

Jocelyn


> 
> I've said it in that other series, but I really think we should be
> having a proper state on the side to deal with those properly.
> 
> Maxime