drm: Check whether the gamma lut has changed before updating

drm_crtc_legacy_gamma_set updates the gamma_lut blob unconditionally,
which leads to unnecessary reprogramming of hardware.

Check whether the blob contents has actually changed before
signalling that it has been updated.

Signed-off-by: Dave Stevenson <[email protected]>

Author: 6by9

drivers/gpu/drm/drm_color_mgmt.c

@@ -326,8 +326,12 @@ static int drm_crtc_legacy_gamma_set(struct drm_crtc *crtc,
 	replaced = drm_property_replace_blob(&crtc_state->degamma_lut,
 					     use_gamma_lut ? NULL : blob);
 	replaced |= drm_property_replace_blob(&crtc_state->ctm, NULL);
-	replaced |= drm_property_replace_blob(&crtc_state->gamma_lut,
+	if (!crtc_state->gamma_lut || !crtc_state->gamma_lut->data ||
+	    memcmp(crtc_state->gamma_lut->data, blob_data, blob->length))
+		replaced |= drm_property_replace_blob(&crtc_state->gamma_lut,
 					      use_gamma_lut ? blob : NULL);
+	else
+		drm_property_blob_put(blob);
 	crtc_state->color_mgmt_changed |= replaced;
 
 	ret = drm_atomic_commit(state);