drm/amd/display: reject atomic commit if setting both plane and CRTC degamma

DC only has pre-blending degamma caps (plane/DPP) that is currently in
use for CRTC/post-blending degamma, so that we don't have HW caps to
perform plane and CRTC degamma at the same time. Reject atomic updates
when serspace sets both plane and CRTC degamma properties.
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_color.c

@@ -944,9 +944,20 @@ int amdgpu_dm_update_plane_color_mgmt(struct dm_crtc_state *crtc,
 	has_crtc_cm_degamma = (crtc->cm_has_degamma || crtc->cm_is_degamma_srgb);
 
 	ret = __set_dm_plane_degamma(plane_state, dc_plane_state);
-	if (ret != -EINVAL)
+	if (ret == -ENOMEM)
 		return ret;
 
+	/* We only have one degamma block available (pre-blending) for the
+	 * whole color correction pipeline, so that we can't actually perform
+	 * plane and CRTC degamma at the same time. Explicitly reject atomic
+	 * updates when userspace sets both plane and CRTC degamma properties.
+	 */
+	if (has_crtc_cm_degamma && ret != -EINVAL){
+		drm_dbg_kms(crtc->base.crtc->dev,
+			    "doesn't support plane and CRTC degamma at the same time\n");
+			return -EINVAL;
+	}
+
 	/* If we are here, it means we don't have plane degamma settings, check
 	 * if we have CRTC degamma waiting for mapping to pre-blending degamma
 	 * block