[PATCH v2 08/10] ALSA: usb-audio: conditional interface altsetting

[Eldad Zack <eldad@fogrefinery.com>]

On some devices, if the endpoint for the other direction is in use,
setting the interface altsetting will shutdown the other (in use)
endpoint.
This patch moves all of the alternate setting operations for pcm
ops to one function which checks if we can do so.

If current alternate is 0, it is safe to set.

Thanks to Clemens Ladisch for pointing out that cur_altsetting
in usb_interface can be used to determine the current altsetting
index.

Signed-off-by: Eldad Zack <eldad@fogrefinery.com>

---
v2:
* Removed get_interface usage.
* Fixed NULL dereference for explicit feedback - now other_subs will
  be set only after testing that subs is not NULL.
---
 sound/usb/pcm.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 72 insertions(+), 10 deletions(-)

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index bdc3325..140e2e4 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -216,6 +216,72 @@ int snd_usb_init_pitch(struct snd_usb_audio *chip, int iface,
 	}
 }
 
+static int get_cur_altset_idx(struct usb_device *dev, int ifnum)
+{
+	struct usb_interface *iface;
+	struct usb_interface_descriptor *altsd;
+
+	if (ifnum == -1)
+		return 0;
+
+	iface = usb_ifnum_to_if(dev, ifnum);
+	if (!iface)
+		return -EINVAL;
+
+	if (!iface->cur_altsetting)
+		return -EINVAL;
+	altsd = &(iface->cur_altsetting->desc);
+
+	return altsd->bAlternateSetting;
+}
+
+static int subs_set_interface(struct snd_usb_substream *subs, int ifnum,
+			      int altset_idx)
+{
+	struct snd_usb_substream *other_subs;
+	int err;
+
+	snd_printdd(KERN_DEBUG "%s: Requested set interface %d alts %d\n",
+		    __func__, ifnum, altset_idx);
+
+	if (subs == NULL)
+		return usb_set_interface(subs->dev, ifnum, altset_idx);
+	other_subs = &(subs->stream->substream[subs->direction ^ 1]);
+
+	if (other_subs->data_endpoint &&
+	    other_subs->data_endpoint->use_count != 0) {
+		int cur_altset_idx = get_cur_altset_idx(subs->dev, ifnum);
+
+		if (cur_altset_idx == altset_idx)
+			return 0;
+
+		if (cur_altset_idx > 0 && altset_idx == 0)
+			return 0;
+	}
+
+	err = usb_set_interface(subs->dev, ifnum, altset_idx);
+	snd_printdd(KERN_DEBUG "%s: Interface %d alts set to %d (err %d)\n",
+		    __func__, ifnum, altset_idx, err);
+	if (err < 0)
+		return err;
+
+	subs->interface = altset_idx == 0 ? -1 : ifnum;
+	subs->altset_idx = altset_idx;
+
+	return 0;
+}
+
+int snd_usb_set_interface(struct snd_usb_substream *subs, int ifnum,
+			  int altset_idx)
+{
+	return subs_set_interface(subs, ifnum, altset_idx);
+}
+
+int snd_usb_close_interface(struct snd_usb_substream *subs, int ifnum)
+{
+	return subs_set_interface(subs, ifnum, 0);
+}
+
 static int start_endpoints(struct snd_usb_substream *subs, bool can_sleep)
 {
 	int err;
@@ -242,9 +308,9 @@ static int start_endpoints(struct snd_usb_substream *subs, bool can_sleep)
 
 		if (subs->data_endpoint->iface != subs->sync_endpoint->iface ||
 		    subs->data_endpoint->alt_idx != subs->sync_endpoint->alt_idx) {
-			err = usb_set_interface(subs->dev,
-						subs->sync_endpoint->iface,
-						subs->sync_endpoint->alt_idx);
+			err = snd_usb_set_interface(subs,
+						    subs->sync_endpoint->iface,
+						    subs->sync_endpoint->alt_idx);
 			if (err < 0) {
 				clear_bit(SUBSTREAM_FLAG_SYNC_EP_STARTED, &subs->flags);
 				snd_printk(KERN_ERR
@@ -467,20 +533,18 @@ 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);
+		err = snd_usb_close_interface(subs, subs->interface);
 		if (err < 0) {
 			snd_printk(KERN_ERR "%d:%d:%d: return to setting 0 failed (%d)\n",
 				dev->devnum, fmt->iface, fmt->altsetting, err);
 			return -EIO;
 		}
-		subs->interface = -1;
-		subs->altset_idx = 0;
 	}
 
 	/* set interface */
 	if (subs->interface != fmt->iface ||
 	    subs->altset_idx != fmt->altset_idx) {
-		err = usb_set_interface(dev, fmt->iface, fmt->altsetting);
+		err = snd_usb_set_interface(subs, fmt->iface, fmt->altsetting);
 		if (err < 0) {
 			snd_printk(KERN_ERR "%d:%d:%d: usb_set_interface failed (%d)\n",
 				   dev->devnum, fmt->iface, fmt->altsetting, err);
@@ -488,8 +552,6 @@ static int set_format(struct snd_usb_substream *subs, struct audioformat *fmt)
 		}
 		snd_printdd(KERN_INFO "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);
 	}
@@ -1196,7 +1258,7 @@ static int snd_usb_pcm_close(struct snd_pcm_substream *substream, int direction)
 	stop_endpoints(subs, true);
 
 	if (!as->chip->shutdown && subs->interface >= 0) {
-		usb_set_interface(subs->dev, subs->interface, 0);
+		snd_usb_close_interface(subs, subs->interface);
 		subs->interface = -1;
 	}
 
-- 
1.8.1.5