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Commit 8a463225 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

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: default avatarTakashi Iwai <tiwai@suse.de>
parent b099b969

sound/usb/pcm.c

+10 −7
Original line number Diff line number Diff line
@@ -509,6 +509,7 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt) 


	/* close the old interface */

	if (subs->interface >= 0 && subs->interface != fmt->iface) {

		if (!subs->stream->chip->keep_iface) {

			err = usb_set_interface(subs->dev, subs->interface, 0);

			if (err < 0) {

				dev_err(&dev->dev,
@@ -516,6 +517,7 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt) 
					fmt->iface, fmt->altsetting, err);

				return -EIO;

			}

		}

		subs->interface = -1;

		subs->altset_idx = 0;

	}
@@ -1253,7 +1255,8 @@ static int snd_usb_pcm_close(struct snd_pcm_substream *substream, int direction) 


	stop_endpoints(subs, true);



	if (subs->interface >= 0 &&

	if (!as->chip->keep_iface &&

	    subs->interface >= 0 &&

	    !snd_usb_lock_shutdown(subs->stream->chip)) {

		usb_set_interface(subs->dev, subs->interface, 0);

		subs->interface = -1;

sound/usb/usbaudio.h

+3 −0
Original line number Diff line number Diff line
@@ -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 */

};