cx25840: add comments explaining what the init() does.

From: Hans Verkuil <hverkuil@xs4all.nl>

Priority: normal

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>

2 files changed, 22 insertions, 0 deletions

diff --git a/linux/drivers/media/video/cx25840/cx25840-core.c b/linux/drivers/media/video/cx25840/cx25840-core.c
index 2860cd702..6d324002a 100644
--- a/linux/drivers/media/video/cx25840/cx25840-core.c
+++ b/linux/drivers/media/video/cx25840/cx25840-core.c
@@ -1120,6 +1120,16 @@ static void log_audio_status(struct i2c_client *client)
 
 /* ----------------------------------------------------------------------- */
 
+/* This init operation must be called to load the driver's firmware.
+   Without this the audio standard detection will fail and you will
+   only get mono.
+
+   Since loading the firmware is often problematic when the driver is
+   compiled into the kernel I recommend postponing calling this function
+   until the first open of the video device. Another reason for
+   postponing it is that loading this firmware takes a long time (seconds)
+   due to the slow i2c bus speed. So it will speed up the boot process if
+   you can avoid loading the fw as long as the video device isn't used.  */
 static int cx25840_init(struct v4l2_subdev *sd, u32 val)
 {
 	struct cx25840_state *state = to_state(sd);
diff --git a/linux/include/media/cx25840.h b/linux/include/media/cx25840.h
index db431d513..2c3fbaa33 100644
--- a/linux/include/media/cx25840.h
+++ b/linux/include/media/cx25840.h
@@ -21,6 +21,18 @@
 #ifndef _CX25840_H_
 #define _CX25840_H_
 
+/* Note that the cx25840 driver requires that the bridge driver calls the
+   v4l2_subdev's init operation in order to load the driver's firmware.
+   Without this the audio standard detection will fail and you will
+   only get mono.
+
+   Since loading the firmware is often problematic when the driver is
+   compiled into the kernel I recommend postponing calling this function
+   until the first open of the video device. Another reason for
+   postponing it is that loading this firmware takes a long time (seconds)
+   due to the slow i2c bus speed. So it will speed up the boot process if
+   you can avoid loading the fw as long as the video device isn't used. */
+
 enum cx25840_video_input {
 	/* Composite video inputs In1-In8 */
 	CX25840_COMPOSITE1 = 1,