Re: [PATCH 1/2] drm: introduce page_flip_timeout()

[Mario Limonciello <mario.limonciello@amd.com>]

On 1/23/2026 8:44 AM, Timur Kristóf wrote:
> On Friday, January 23, 2026 2:52:44 PM Central European Standard Time
> Christian König wrote:
>> On 1/23/26 01:05, Hamza Mahfooz wrote:
>>> There should be a mechanism for drivers to respond to flip_done
>>> time outs.
>>
> 

When there is a display hang, I think that resetting the GPU IP is 
really heavy handed.  I second what Alex said - Why not instead just 
reset DCN?  I would think move DCN into D3 and back out should be enough 
if trying to use something to recover.

> I am adding Harry and Mario to this email as they are more familiar with this.
> 
>> I can only see two reasons why you could run into a timeout:
>>
>> 1. A dma_fence never signals.
>> 	How that should be handled is already well documented and doesn't
> require
>> any of this.
> 
> Page flip timeouts have nothing to do with fence timeouts.
> A page flip timeout can occur even when all fences of all job submissions
> complete correctly and on time.
> 
>>
>> 2. A coding error in the vblank or page flip handler leading to waiting
>> forever. In that case calling back into the driver doesn't help either.
> 
> At the moment, a page flip timeout will leave the whole system in a hung state
> and the driver does not even attempt to recover it in any way, it just stops
> doing anything, which is unacceptable and I'm pretty surprised that it was
> left like that for so long.
> 
> Note that we have approximately a hundred bug reports open on the drm/amd bug
> tracker about "random" page flip timeouts. It affects a lot of users.

Yeah I would much rather leave some messages in the log that this 
happened and see a recovery occur than a hang.

> 
>>
>> So as far as I can see the whole approach doesn't make any sense at all.
> 
> Actually this approach was proposed as a solution at XDC 2025 in Harry's
> presentation, "DRM calls driver callback to attempt recovery", see page 9 in
> this slide deck:
> 
> https://indico.freedesktop.org/event/10/contributions/431/attachments/
> 267/355/2025%20XDC%20Hackfest%20Update%20v1.2.pdf
> 
> If you disagree with Harry, please make a counter-proposal.

Hamza - since you seem to have a "workload" that can run overnight and 
this series recovers, can you try what Alex said and do a dc_suspend() 
and dc_resume() for failure?

Make sure you log a message so you can know it worked.

> 
> Thanks,
> Timur
> 
> 
> 
>>
>>> Since, as it stands it is possible for the display
>>> to stall indefinitely, necessitating a hard reset. So, introduce
>>> a new crtc callback that is called by
>>> drm_atomic_helper_wait_for_flip_done() to give drivers a shot
>>> at recovering from page flip timeouts.
>>>
>>> Signed-off-by: Hamza Mahfooz <someguy@effective-light.com>
>>> ---
>>>
>>>   drivers/gpu/drm/drm_atomic_helper.c | 6 +++++-
>>>   include/drm/drm_crtc.h              | 9 +++++++++
>>>   2 files changed, 14 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_atomic_helper.c
>>> b/drivers/gpu/drm/drm_atomic_helper.c index 5840e9cc6f66..3a144c324b19
>>> 100644
>>> --- a/drivers/gpu/drm/drm_atomic_helper.c
>>> +++ b/drivers/gpu/drm/drm_atomic_helper.c
>>> @@ -1881,9 +1881,13 @@ void drm_atomic_helper_wait_for_flip_done(struct
>>> drm_device *dev,>
>>>   			continue;
>>>   		
>>>   		ret = wait_for_completion_timeout(&commit->flip_done, 10
> * HZ);
>>>
>>> -		if (ret == 0)
>>> +		if (!ret) {
>>>
>>>   			drm_err(dev, "[CRTC:%d:%s] flip_done timed
> out\n",
>>>   			
>>>   				crtc->base.id, crtc->name);
>>>
>>> +
>>> +			if (crtc->funcs->page_flip_timeout)
>>> +				crtc->funcs-
>> page_flip_timeout(crtc);
>>> +		}
>>>
>>>   	}
>>>   	
>>>   	if (state->fake_commit)
>>>
>>> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
>>> index 66278ffeebd6..45dc5a76e915 100644
>>> --- a/include/drm/drm_crtc.h
>>> +++ b/include/drm/drm_crtc.h
>>> @@ -609,6 +609,15 @@ struct drm_crtc_funcs {
>>>
>>>   				uint32_t flags, uint32_t target,
>>>   				struct drm_modeset_acquire_ctx
> *ctx);
>>>
>>> +	/**
>>> +	 * @page_flip_timeout:
>>> +	 *
>>> +	 * This optional hook is called if &drm_crtc_commit.flip_done times
> out,
>>> +	 * and can be used by drivers to attempt to recover from a page
> flip
>>> +	 * timeout.
>>> +	 */
>>> +	void (*page_flip_timeout)(struct drm_crtc *crtc);
>>> +
>>>
>>>   	/**
>>>   	
>>>   	 * @set_property:
>>>   	 *
> 
> 
> 
>