Re: [Intel-gfx] [PATCH] drm/atomic-helper: Don't set deadline for modesets

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Apr 05, 2023 at 10:16:50AM +0200, Daniel Vetter wrote:
> If the crtc is being switched on or off then the semantics of
> computing the timestampe of the next vblank is somewhat ill-defined.
> And indeed, the code splats with a warning in the timestamp
> computation code. Specifically it hits the check to make sure that
> atomic drivers have full set up the timing constants in the drm_vblank
> structure, and that's just not the case before the crtc is actually
> on.
> 
> For robustness it seems best to just not set deadlines for modesets.
> 
> Link: https://lore.kernel.org/dri-devel/dfc21f18-7e1e-48f0-c05a-d659b9c90b91@linaro.org/
> Fixes: d39e48ca80c0 ("drm/atomic-helper: Set fence deadline for vblank")
> Cc: Rob Clark <robdclark@chromium.org>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Reported-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> Tested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> # test patch only
> Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index f21b5a74176c..6640d80d84f3 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1528,6 +1528,9 @@ static void set_fence_deadline(struct drm_device *dev,
>  	for_each_new_crtc_in_state (state, crtc, new_crtc_state, i) {
>  		ktime_t v;
>  
> +		if (drm_atomic_crtc_needs_modeset(new_crtc_state))
> +			continue;

Should this stuff also be skipped when !new_crtc_state->active?
I didn't actually check what drm_crtc_next_vblank_start() ends
up doing in that case.

> +
>  		if (drm_crtc_next_vblank_start(crtc, &v))
>  			continue;
>  
> -- 
> 2.40.0

-- 
Ville Syrjälä
Intel