From 6f3e0c4c5f8395a1348014fbda347e0fa87c999c Mon Sep 17 00:00:00 2001
From: Dave Stevenson <dave.stevenson@raspberrypi.com>
Date: Tue, 2 Nov 2021 16:01:36 +0000
Subject: [PATCH] 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 <dave.stevenson@raspberrypi.com>
---
 drivers/gpu/drm/drm_color_mgmt.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -332,7 +332,9 @@ static int drm_crtc_legacy_gamma_set(str
 	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);
 	crtc_state->color_mgmt_changed |= replaced;
 
