1 files changed, 33 insertions, 0 deletions
diff --git a/target/linux/bcm27xx/patches-5.15/950-0562-drm-Check-whether-the-gamma-lut-has-changed-before-u.patch b/target/linux/bcm27xx/patches-5.15/950-0562-drm-Check-whether-the-gamma-lut-has-changed-before-u.patch
new file mode 100644
index 0000000000..22ef7b6143
--- /dev/null
+++ b/target/linux/bcm27xx/patches-5.15/950-0562-drm-Check-whether-the-gamma-lut-has-changed-before-u.patch
@@ -0,0 +1,33 @@
+From 190eaf4f8d95196b1b66c7c356d28643a6355039 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 | 6 +++++-
+ 1 file changed, 5 insertions(+), 1 deletion(-)
+
+--- a/drivers/gpu/drm/drm_color_mgmt.c
++++ b/drivers/gpu/drm/drm_color_mgmt.c
+@@ -326,8 +326,12 @@ 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);
++	else
++		drm_property_blob_put(blob);
+ 	crtc_state->color_mgmt_changed |= replaced;
+ 
+ 	ret = drm_atomic_commit(state);