V4L/DVB (3254): Don't reprogram the video standard if it is unchanged.

- Don't reprogram the video standard if the new standard
equals the old standard.
Signed-off-by: NHans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: NMauro Carvalho Chehab <mchehab@brturbo.com.br>

drivers/media/video/saa7115.c

@@ -668,6 +668,16 @@ static void saa7115_set_v4lstd(struct i2c_client *client, v4l2_std_id std)
 	struct saa7115_state *state = i2c_get_clientdata(client);
 	int taskb = saa7115_read(client, 0x80) & 0x10;
 
+	/* Prevent unnecessary standard changes. During a standard
+	   change the I-Port is temporarily disabled. Any devices
+	   reading from that port can get confused.
+	   Note that VIDIOC_S_STD is also used to switch from
+	   radio to TV mode, so if a VIDIOC_S_STD is broadcast to
+	   all I2C devices then you do not want to have an unwanted
+	   side-effect here. */
+	if (std == state->std)
+		return;
+
 	// This works for NTSC-M, SECAM-L and the 50Hz PAL variants.
 	if (std & V4L2_STD_525_60) {
 		saa7115_dbg("decoder set standard 60 Hz\n");