drm: apple: Reduce log spam about busy command channel

The most likely cause for this is an unexpected callback form which the
current driver doesn't recover. Warn only once about it.

Signed-off-by: Janne Grunau <j@jannau.net>

Author: jannau

drivers/gpu/drm/apple/dcp-internal.h

@@ -71,6 +71,8 @@ struct dcp_channel {
 
 	/* Current depth of the call stack. Less than DCP_MAX_CALL_DEPTH */
 	u8 depth;
+	/* Already warned about busy channel */
+	bool warned_busy;
 };
 
 struct dcp_fb_reference {

drivers/gpu/drm/apple/iomfb.c

@@ -482,12 +482,17 @@ void dcp_flush(struct drm_crtc *crtc, struct drm_atomic_state *state)
 
 	if (dcp_channel_busy(&dcp->ch_cmd))
 	{
-		dev_err(dcp->dev, "unexpected busy command channel\n");
+		if (!dcp->ch_cmd.warned_busy) {
+			dev_err(dcp->dev, "unexpected busy command channel\n");
+			dcp->ch_cmd.warned_busy = true;
+		}
 		/* HACK: issue a delayed vblank event to avoid timeouts in
 		 * drm_atomic_helper_wait_for_vblanks().
 		 */
 		schedule_work(&dcp->vblank_wq);
 		return;
+	} else if (dcp->ch_cmd.warned_busy) {
+		dcp->ch_cmd.warned_busy = false;
 	}
 
 	switch (dcp->fw_compat) {