media: imx-csi: Skip first few frames from a BT.656 source

Some BT.656 sensors (e.g. ADV718x) transmit frames with unstable BT.656
sync codes after initial power on. This confuses the imx CSI,resulting
in vertical and/or horizontal sync issues. Skip the first 20 frames
to avoid the unstable sync codes.

[fabio: fixed checkpatch warning and increased the frame skipping to 20]
Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/staging/media/imx/imx-media-csi.c

@@ -750,9 +750,10 @@ static int csi_setup(struct csi_priv *priv)
 
 static int csi_start(struct csi_priv *priv)
 {
-	struct v4l2_fract *output_fi;
+	struct v4l2_fract *input_fi, *output_fi;
 	int ret;
 
+	input_fi = &priv->frame_interval[CSI_SINK_PAD];
 	output_fi = &priv->frame_interval[priv->active_output_pad];
 
 	/* start upstream */
@@ -761,6 +762,17 @@ static int csi_start(struct csi_priv *priv)
 	if (ret)
 		return ret;
 
+	/* Skip first few frames from a BT.656 source */
+	if (priv->upstream_ep.bus_type == V4L2_MBUS_BT656) {
+		u32 delay_usec, bad_frames = 20;
+
+		delay_usec = DIV_ROUND_UP_ULL((u64)USEC_PER_SEC *
+			input_fi->numerator * bad_frames,
+			input_fi->denominator);
+
+		usleep_range(delay_usec, delay_usec + 1000);
+	}
+
 	if (priv->dest == IPU_CSI_DEST_IDMAC) {
 		ret = csi_idmac_start(priv);
 		if (ret)