[media] radio-si470x: Don't unnecesarily read registers on G_TUNER

Reading registers from the pcear USB dongles with the si470x causes a
loud pop (and an alsa buffer overrun). Since most radio apps periodically
call G_TUNER to update mono/stereo, signal and afc status this leads
to the music . pop . music . pop . music -> not good.

On the internet there is an howto for flashing the pcear with a newer
firmware from the silabs reference boardto fix this, but:
1) This howto relies on a special version of the driver which allows
   firmware flashing
2) We should try to avoid the answer to a bug report being upgrade your
   firmware, if at all possible
3) Windows does not suffer from the pop sounds

After a quick look at the driver I found at that the register reads are
not necessary at all, as the device gives us the necessary status through
usb interrupt packets, and the driver already uses these!

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/drivers/media/radio/si470x/radio-si470x-common.c b/drivers/media/radio/si470x/radio-si470x-common.c
index d485b79222fd..5dbb897e14de 100644
--- a/drivers/media/radio/si470x/radio-si470x-common.c
+++ b/drivers/media/radio/si470x/radio-si470x-common.c
@@ -583,14 +583,16 @@ static int si470x_vidioc_g_tuner(struct file *file, void *priv,
 		struct v4l2_tuner *tuner)
 {
 	struct si470x_device *radio = video_drvdata(file);
-	int retval;
+	int retval = 0;
 
 	if (tuner->index != 0)
 		return -EINVAL;
 
-	retval = si470x_get_register(radio, STATUSRSSI);
-	if (retval < 0)
-		return retval;
+	if (!radio->status_rssi_auto_update) {
+		retval = si470x_get_register(radio, STATUSRSSI);
+		if (retval < 0)
+			return retval;
+	}
 
 	/* driver constants */
 	strcpy(tuner->name, "FM");