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>

diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index 8c225fb..ec4a9a0 100644 (file)
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -313,7 +313,11 @@ static int drm_crtc_legacy_gamma_set(struct drm_crtc *crtc,
        /* Set GAMMA_LUT and reset DEGAMMA_LUT and CTM */
        replaced = drm_property_replace_blob(&crtc_state->degamma_lut, NULL);
        replaced |= drm_property_replace_blob(&crtc_state->ctm, NULL);
-       replaced |= drm_property_replace_blob(&crtc_state->gamma_lut, blob);
+       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, blob);
+       else
+               drm_property_blob_put(blob);
        crtc_state->color_mgmt_changed |= replaced;
 
        ret = drm_atomic_commit(state);