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>

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;

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;

drivers/staging/omapdrm/omap_crtc.c

@@ -36,12 +36,6 @@ struct omap_crtc {
 	struct drm_framebuffer *old_fb;
 };
 
-static void omap_crtc_gamma_set(struct drm_crtc *crtc,
-		u16 *red, u16 *green, u16 *blue, uint32_t start, uint32_t size)
-{
-	/* not supported.. at least not yet */
-}
-
 static void omap_crtc_destroy(struct drm_crtc *crtc)
 {
 	struct omap_crtc *omap_crtc = to_omap_crtc(crtc);
@@ -198,7 +192,6 @@ static int omap_crtc_page_flip_locked(struct drm_crtc *crtc,
 }
 
 static const struct drm_crtc_funcs omap_crtc_funcs = {
-	.gamma_set = omap_crtc_gamma_set,
 	.set_config = drm_crtc_helper_set_config,
 	.destroy = omap_crtc_destroy,
 	.page_flip = omap_crtc_page_flip_locked,