ALSA: usb: handle descriptor with SYNC_NONE illegal value

The M-Audio Transit exposes an interface with a SYNC_NONE attribute.
This is not a valid value according to the USB audio classspec. However
there is a sync endpoint associated to this record. Changing the logic to
try to use this sync endpoint allows for seamless transitions between
altset 2 and altset 3. If any errors happen, the behavior remains the same.

$ more /proc/asound/card1/stream0
M-Audio Transit USB at usb-0000:00:14.0-2, full speed : USB Audio

Playback:
  Status: Stop
  Interface 1
    Altset 1
    Format: S24_3LE
    Channels: 2
    Endpoint: 3 OUT (ADAPTIVE)
    Rates: 48001 - 96000 (continuous)
  Interface 1
    Altset 2
    Format: S24_3LE
    Channels: 2
    Endpoint: 3 OUT (NONE)
    Rates: 8000 - 48000 (continuous)
  Interface 1
    Altset 3
    Format: S16_LE
    Channels: 2
    Endpoint: 3 OUT (ASYNC)
    Rates: 8000 - 48000 (continuous)

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 7fb17c8eb49ddcc3d15c8c1d52e11e4fd5f270d2..30797269d5aade31fb44d781a6c36d3f9f5a4f1f 100644 (file)
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -412,10 +412,17 @@ static int set_sync_endpoint(struct snd_usb_substream *subs,
        if (altsd->bNumEndpoints < 2)
                return 0;
 
-       if ((is_playback && attr != USB_ENDPOINT_SYNC_ASYNC) ||
+       if ((is_playback && (attr == USB_ENDPOINT_SYNC_SYNC ||
+                            attr == USB_ENDPOINT_SYNC_ADAPTIVE)) ||
            (!is_playback && attr != USB_ENDPOINT_SYNC_ADAPTIVE))
                return 0;
 
+       /*
+        * In case of illegal SYNC_NONE for OUT endpoint, we keep going to see
+        * if we don't find a sync endpoint, as on M-Audio Transit. In case of
+        * error fall back to SYNC mode and don't create sync endpoint
+        */
+
        /* check sync-pipe endpoint */
        /* ... and check descriptor size before accessing bSynchAddress
           because there is a version of the SB Audigy 2 NX firmware lacking
@@ -429,6 +436,8 @@ static int set_sync_endpoint(struct snd_usb_substream *subs,
                           get_endpoint(alts, 1)->bmAttributes,
                           get_endpoint(alts, 1)->bLength,
                           get_endpoint(alts, 1)->bSynchAddress);
+               if (is_playback && attr == USB_ENDPOINT_SYNC_NONE)
+                       return 0;
                return -EINVAL;
        }
        ep = get_endpoint(alts, 1)->bEndpointAddress;
@@ -439,6 +448,8 @@ static int set_sync_endpoint(struct snd_usb_substream *subs,
                        "%d:%d : invalid sync pipe. is_playback %d, ep %02x, bSynchAddress %02x\n",
                           fmt->iface, fmt->altsetting,
                           is_playback, ep, get_endpoint(alts, 0)->bSynchAddress);
+               if (is_playback && attr == USB_ENDPOINT_SYNC_NONE)
+                       return 0;
                return -EINVAL;
        }
 
@@ -450,8 +461,11 @@ static int set_sync_endpoint(struct snd_usb_substream *subs,
                                                   implicit_fb ?
                                                        SND_USB_ENDPOINT_TYPE_DATA :
                                                        SND_USB_ENDPOINT_TYPE_SYNC);
-       if (!subs->sync_endpoint)
+       if (!subs->sync_endpoint) {
+               if (is_playback && attr == USB_ENDPOINT_SYNC_NONE)
+                       return 0;
                return -EINVAL;
+       }
 
        subs->data_endpoint->sync_master = subs->sync_endpoint;