ALSA: usb-audio: Add keep_iface flag

Introduce a new flag to struct snd_usb_audio for allowing the device
to skip usb_set_interface() calls at changing or closing the stream.
As of this patch, the flag is nowhere set, so it's just a place
holder.  The dynamic switching will be added in the following patch.

A background information for this change:

Dell WD15 dock with Realtek chip gives a very long pause at each time
the driver changes the altset, which eventually happens at every PCM
stream open/close and parameter change.  As the long pause happens in
each usb_set_interface() call, there is nothing we can do as long as
it's called.  The workaround is to reduce calling it as much as
possible, and this flag indicates that behavior.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 3 insertions, 0 deletions

diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h
index 4d5c89a7ba2b..32f4a5425536 100644
--- a/sound/usb/usbaudio.h
+++ b/sound/usb/usbaudio.h
@@ -59,6 +59,9 @@ struct snd_usb_audio {
 
 	int setup;			/* from the 'device_setup' module param */
 	bool autoclock;			/* from the 'autoclock' module param */
+	bool keep_iface;		/* keep interface/altset after closing
+					 * or parameter change
+					 */
 
 	struct usb_host_interface *ctrl_intf;	/* the audio control interface */
 };