drm/vc4: kms: Ignore atomic_flush if we're disabled

atomic_flush will be called for each CRTC even if they aren't enabled.

The whole code we have there will thus run without a properly affected
channel, which can then result in all sorts of weird behaviour.

Fortunately, the DRM_PLANE_COMMIT_ACTIVE_ONLY flag will skip the CRTC
atomic_begin and atomic_flush, and the planes atomic_update, if they
aren't enabled.

Our plane atomic_update is a nop, and atomic_begin will copy the current
HVS channel to the vc4_crtc structure for the interrupt handler to
consume, but the handler won't run if the CRTC is disabled. So in the
end, it will only skip our CRTC atomic_flush, which is what we want.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20220331143744.777652-7-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_kms.c

@@ -409,7 +409,8 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
 	else
 		vc4_hvs_pv_muxing_commit(vc4, state);
 
-	drm_atomic_helper_commit_planes(dev, state, 0);
+	drm_atomic_helper_commit_planes(dev, state,
+					DRM_PLANE_COMMIT_ACTIVE_ONLY);
 
 	drm_atomic_helper_commit_modeset_enables(dev, state);