drm/sti: do not post GDP command if no update

Do not process update requests with unmodified parameters.

This typically happens when the driver is called with legacy
(non-atomic) IOCTL : in that case atomic_update() is called multiple
times with the same parameters.
Signed-off-by: Vincent Abriou <vincent.abriou@st.com>

drivers/gpu/drm/sti/sti_gdp.c

@@ -708,6 +708,21 @@ static void sti_gdp_atomic_update(struct drm_plane *drm_plane,
 	if (!crtc || !fb)
 		return;
 
+	if ((oldstate->fb == state->fb) &&
+	    (oldstate->crtc_x == state->crtc_x) &&
+	    (oldstate->crtc_y == state->crtc_y) &&
+	    (oldstate->crtc_w == state->crtc_w) &&
+	    (oldstate->crtc_h == state->crtc_h) &&
+	    (oldstate->src_x == state->src_x) &&
+	    (oldstate->src_y == state->src_y) &&
+	    (oldstate->src_w == state->src_w) &&
+	    (oldstate->src_h == state->src_h)) {
+		/* No change since last update, do not post cmd */
+		DRM_DEBUG_DRIVER("No change, not posting cmd\n");
+		plane->status = STI_PLANE_UPDATED;
+		return;
+	}
+
 	if (!gdp->vtg) {
 		struct sti_compositor *compo = dev_get_drvdata(gdp->dev);
 		struct sti_mixer *mixer = to_sti_mixer(crtc);