Re: [PATCH v6 1/2] drm/atomic: attempt full modeset on page flip timeout

[Hamza Mahfooz]

On Wed, May 06, 2026 at 09:47:05PM +0300, Ville Syrjälä wrote:
> On Tue, May 05, 2026 at 02:20:57PM -0400, Hamza Mahfooz wrote:
> > We should try to recover from page flip timeouts. Forcing
> > a full modeset should be generic across all atomic KMS drivers,
> > so try that first.
> > 
> > Signed-off-by: Hamza Mahfooz <someguy@xxxxxxxxxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/drm_atomic_helper.c | 49 +++++++++++++++++++++++++++--
> >  1 file changed, 46 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index a768398a1884..7ee9d52f63c5 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -1926,6 +1926,43 @@ drm_atomic_helper_wait_for_vblanks(struct drm_device *dev,
> >  }
> >  EXPORT_SYMBOL(drm_atomic_helper_wait_for_vblanks);
> >  
> > +static int force_full_modeset(struct drm_crtc *crtc)
> > +{
> > +	struct drm_modeset_acquire_ctx ctx;
> > +	struct drm_crtc_state *crtc_state;
> > +	struct drm_atomic_state *state;
> > +	int ret;
> > +	int err;
> > +
> > +	if (drm_atomic_crtc_needs_modeset(crtc->state))
> > +		return -EBUSY;
> > +
> > +	DRM_MODESET_LOCK_ALL_BEGIN(crtc->dev, ctx, 0, err);
> > +	state = drm_atomic_state_alloc(crtc->dev);
> > +	if (!state)
> > +		return -ENOMEM;
> > +
> > +	state->acquire_ctx = &ctx;
> > +
> > +	crtc_state = drm_atomic_get_crtc_state(state, crtc);
> > +	if (IS_ERR(crtc_state)) {
> > +		ret = PTR_ERR(crtc_state);
> > +		goto out;
> > +	}
> > +
> > +	crtc_state->mode_changed = true;
> > +
> > +	drm_info(crtc->dev,
> > +		 "[CRTC:%d:%s] Attempting force full modeset...\n",
> > +		 crtc->base.id, crtc->name);
> > +
> > +	ret = drm_atomic_commit(state);
> > +out:
> > +	drm_atomic_state_put(state);
> > +	DRM_MODESET_LOCK_ALL_END(crtc->dev, ctx, err);
> > +	return ret;
> > +}
> > +
> >  /**
> >   * drm_atomic_helper_wait_for_flip_done - wait for all page flips to be done
> >   * @dev: DRM device
> > @@ -1949,17 +1986,23 @@ void drm_atomic_helper_wait_for_flip_done(struct drm_device *dev,
> >  
> >  	for (i = 0; i < dev->mode_config.num_crtc; i++) {
> >  		struct drm_crtc_commit *commit = state->crtcs[i].commit;
> > -		int ret;
> >  
> >  		crtc = state->crtcs[i].ptr;
> >  
> >  		if (!crtc || !commit)
> >  			continue;
> >  
> > -		ret = wait_for_completion_timeout(&commit->flip_done, 10 * HZ);
> > -		if (ret == 0)
> > +		if (!wait_for_completion_timeout(&commit->flip_done, 10 * HZ)) {
> > +			int ret;
> >  			drm_err(dev, "[CRTC:%d:%s] flip_done timed out\n",
> >  				crtc->base.id, crtc->name);
> > +
> > +			ret = force_full_modeset(crtc);
> 
> This looks like some kind of ugly hack to paper over a driver bug.
> I really don't want this for i915/xe because all it'll end up doing
> is make it harder to debug any real issues.

In that case, would you be okay with having
drm_atomic_helper_wait_for_flip_done() return an error code, or did you
have something else in mind?

> 
> > +			if (ret)
> > +				drm_err(dev,
> > +					"[CRTC:%d:%s] force full modeset failed! ret=%d\n",
> > +					crtc->base.id, crtc->name, ret);
> > +		}
> >  	}
> >  
> >  	if (state->fake_commit)
> > -- 
> > 2.54.0
> 
> -- 
> Ville Syrjälä
> Intel