drm/atomic-helper: Don't set deadline for modesets

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.

v2: Also skip on inactive crtc (Ville)

Link: https://lore.kernel.org/dri-devel/dfc21f18-7e1e-48f0-c05a-d659b9c90b91@linaro.org/
Fixes: d39e48c ("drm/atomic-helper: Set fence deadline for vblank")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
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>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230405133105.947834-1-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_atomic_helper.c

@@ -1528,6 +1528,12 @@ 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;
+
+		if (!new_crtc_state->active)
+			continue;
+
 		if (drm_crtc_next_vblank_start(crtc, &v))
 			continue;