drm: Make the CRTC gamma_set operation optional

Drivers for hardware without gamma support should not be forced to
implement a no-op gamma set operation.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Rob Clark <rob.clark@linaro.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

2 files changed, 8 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 404597e8150a..6cb47d9f0ca2 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -3332,6 +3332,11 @@ int drm_mode_gamma_set_ioctl(struct drm_device *dev,
         }
         crtc = obj_to_crtc(obj);
 
+        if (crtc->funcs->gamma_set == NULL) {
+                ret = -ENOSYS;
+                goto out;
+        }
+
         /* memcpy into gamma store */
         if (crtc_lut->gamma_size != crtc->gamma_size) {
                 ret = -EINVAL;
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 9b773d51cff5..5683b7fdd746 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -136,6 +136,9 @@ static void drm_fb_helper_restore_lut_atomic(struct drm_crtc *crtc)
 {
         uint16_t *r_base, *g_base, *b_base;
 
+        if (crtc->funcs->gamma_set == NULL)
+                return;
+
         r_base = crtc->gamma_store;
         g_base = r_base + crtc->gamma_size;
         b_base = g_base + crtc->gamma_size;