ALSA: usb-audio: Avoid superfluous usb_set_interface() calls

This is a preliminary change for the upcoming quirk implementation.

Currently USB-audio driver tries to call usb_set_interface() whenever
the format change with interface/altset modification happens.  In this
patch, the check is replaced with the comparison of cur_altsetting and
the targeted altsetting pointer, so that the driver may skip the
unnecessary function calls.

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

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index ad39b3cca2476b778e4be5d1227b5255587043a3..ae7d8a0a0a0a32bae4100c48bccd024ca88f3d09 100644 (file)
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -499,7 +499,7 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
        iface = usb_ifnum_to_if(dev, fmt->iface);
        if (WARN_ON(!iface))
                return -EINVAL;
-       alts = &iface->altsetting[fmt->altset_idx];
+       alts = usb_altnum_to_altsetting(iface, fmt->altsetting);
        altsd = get_iface_desc(alts);
        if (WARN_ON(altsd->bAlternateSetting != fmt->altsetting))
                return -EINVAL;
@@ -521,9 +521,7 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
        }
 
        /* set interface */
-       if (subs->interface != fmt->iface ||
-           subs->altset_idx != fmt->altset_idx) {
-
+       if (iface->cur_altsetting != alts) {
                err = snd_usb_select_mode_quirk(subs, fmt);
                if (err < 0)
                        return -EIO;
@@ -537,12 +535,11 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
                }
                dev_dbg(&dev->dev, "setting usb interface %d:%d\n",
                        fmt->iface, fmt->altsetting);
-               subs->interface = fmt->iface;
-               subs->altset_idx = fmt->altset_idx;
-
                snd_usb_set_interface_quirk(dev);
        }
 
+       subs->interface = fmt->iface;
+       subs->altset_idx = fmt->altset_idx;
        subs->data_endpoint = snd_usb_add_endpoint(subs->stream->chip,
                                                   alts, fmt->endpoint, subs->direction,
                                                   SND_USB_ENDPOINT_TYPE_DATA);