drm/i915: Unlink NV12 planes earlier

unlink_nv12_plane() will clobber parts of the plane state
potentially already set up by plane_atomic_check(), so we
must make sure not to call the two in the wrong order.
The problem happens when a plane previously selected as
a Y plane is now configured as a normal plane by user space.
plane_atomic_check() will first compute the proper plane
state based on the userspace request, and unlink_nv12_plane()
later clears some of the state.

This used to work on account of unlink_nv12_plane() skipping
the state clearing based on the plane visibility. But I removed
that check, thinking it was an impossible situation. Now when
that situation happens unlink_nv12_plane() will just WARN
and proceed to clobber the state.

Rather than reverting to the old way of doing things, I think
it's more clear if we unlink the NV12 planes before we even
compute the new plane state.

Cc: [email protected]
Reported-by: Khaled Almahallawy <[email protected]>
Closes: https://lore.kernel.org/intel-gfx/[email protected]/
Tested-by: Khaled Almahallawy <[email protected]>
Fixes: 6a01df2 ("drm/i915: Remove pointless visible check in unlink_nv12_plane()")
Signed-off-by: Ville Syrjälä <[email protected]>
Link: https://patch.msgid.link/[email protected]
Reviewed-by: Uma Shankar <[email protected]>
(cherry picked from commit 017ecd0)
Signed-off-by: Joonas Lahtinen <[email protected]>

Author: vsyrjala

drivers/gpu/drm/i915/display/intel_plane.c

@@ -436,11 +436,16 @@ void intel_plane_copy_hw_state(struct intel_plane_state *plane_state,
 		drm_framebuffer_get(plane_state->hw.fb);
 }
 
+static void unlink_nv12_plane(struct intel_crtc_state *crtc_state,
+			      struct intel_plane_state *plane_state);
+
 void intel_plane_set_invisible(struct intel_crtc_state *crtc_state,
 			       struct intel_plane_state *plane_state)
 {
 	struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
 
+	unlink_nv12_plane(crtc_state, plane_state);
+
 	crtc_state->active_planes &= ~BIT(plane->id);
 	crtc_state->scaled_planes &= ~BIT(plane->id);
 	crtc_state->nv12_planes &= ~BIT(plane->id);
@@ -1513,6 +1518,9 @@ static void unlink_nv12_plane(struct intel_crtc_state *crtc_state,
 	struct intel_display *display = to_intel_display(plane_state);
 	struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
 
+	if (!plane_state->planar_linked_plane)
+		return;
+
 	plane_state->planar_linked_plane = NULL;
 
 	if (!plane_state->is_y_plane)
@@ -1550,8 +1558,7 @@ static int icl_check_nv12_planes(struct intel_atomic_state *state,
 		if (plane->pipe != crtc->pipe)
 			continue;
 
-		if (plane_state->planar_linked_plane)
-			unlink_nv12_plane(crtc_state, plane_state);
+		unlink_nv12_plane(crtc_state, plane_state);
 	}
 
 	if (!crtc_state->nv12_planes)