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ALSA: usb-audio: Add keep_iface flag

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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>
This commit is contained in:
Takashi Iwai 2018-05-02 10:04:27 +02:00
parent b099b9693d
commit 8a463225b1
2 changed files with 13 additions and 7 deletions
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17
sound/usb/pcm.c
View file

@ -509,12 +509,14 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
/* close the old interface */
if (subs->interface >= 0 && subs->interface != fmt->iface) {
err = usb_set_interface(subs->dev, subs->interface, 0);
if (err < 0) {
dev_err(&dev->dev,
"%d:%d: return to setting 0 failed (%d)\n",
fmt->iface, fmt->altsetting, err);
return -EIO;
if (!subs->stream->chip->keep_iface) {
err = usb_set_interface(subs->dev, subs->interface, 0);
if (err < 0) {
dev_err(&dev->dev,
"%d:%d: return to setting 0 failed (%d)\n",
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;

3
sound/usb/usbaudio.h
View file

@ -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 */
};