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

["Timur Kristóf" <timur.kristof@gmail.com>]

On Thursday, January 29, 2026 11:06:11 AM Central European Standard Time 
Michel Dänzer wrote:
> >>> 
> >>> Christian, why would the CRTC be turned off?
> >> 
> >> Exactly that's the question we need to answer.
> >> 
> >> But from what you describe the CRTC keeps on, just doesn't send any more
> >> vblank events.> 
> > The vblank interrupt source getting accidentally disabled might be one
> > possible cause though.
> Another possibility is that test-only commits with the
> DRM_MODE_ATOMIC_TEST_ONLY flag (which can happen in parallel while the
> kernel is processing a "real" commit) accidentally have side effects on the
> current kernel state, resulting in the "real" commit failing to do
> something it should. There have been bugs like that in the amdgpu DM code
> before.
> 
> 
> Anyway, this is all speculation. Somebody just needs to dig in and get to
> the bottom of why the commits aren't getting completed.

Yes, I agree.

However, just like we do with ring timeouts, we also need to be prepared for 
the situation where a page flip timeout happens and we should try to recover 
from it. And if it isn't recoverable, fall back to GPU reset.

I strongly suspect that there are many different issues depending on the 
hardware generation and display configuration. There isn't going to be a silver 
bullet to fix all of them, and in case it cannot be fixed, I think a GPU reset 
is the right thing to do - it's drastic, but still better than letting the 
machine just freeze irrecoverably.

One example of such a bug was fixed by 6cbe6e072c5d where DC was trying to use 
an interrupt that didn't exist on some hardware. This type of bug would be 
impossible for userspace to solve in any way, but a GPU reset would have 
helped to recover the machine into a usable state.

Another example would be Strix Halo with adaptive sync and/or tearing updates 
enabled, which 100% reproduces a page flip timeout for me. I haven't had time 
to investigate that one just yet.

Timur