[ALSA] usb-audio - fix synchronization packet interval with Audigy 2 NX

USB generic driver
When a device does not provide the bRefresh field in its audio endpoint
descriptors, use the bInterval field instead.

Furthermore, increase the number of sync URBs for better queueing.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

1 files changed, 7 insertions, 2 deletions

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 076da19a9e28..a82412b8790d 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -98,7 +98,7 @@ MODULE_PARM_DESC(async_unlink, "Use async unlink mode.");
 #define MAX_PACKS       10
 #define MAX_PACKS_HS    (MAX_PACKS * 8) /* in high speed mode */
 #define MAX_URBS        5       /* max. 20ms long packets */
-#define SYNC_URBS       2       /* always two urbs for sync */
+#define SYNC_URBS       4       /* always four urbs for sync */
 #define MIN_PACKS_URB   1       /* minimum 1 packet per urb */
 
 typedef struct snd_usb_substream snd_usb_substream_t;
@@ -1240,8 +1240,13 @@ static int set_format(snd_usb_substream_t *subs, struct audioformat *fmt)
                     get_endpoint(alts, 1)->bRefresh >= 1 &&
                     get_endpoint(alts, 1)->bRefresh <= 9)
                         subs->syncinterval = get_endpoint(alts, 1)->bRefresh;
-                else
+                else if (snd_usb_get_speed(subs->dev) == USB_SPEED_FULL)
                         subs->syncinterval = 1;
+                else if (get_endpoint(alts, 1)->bInterval >= 1 &&
+                         get_endpoint(alts, 1)->bInterval <= 16)
+                        subs->syncinterval = get_endpoint(alts, 1)->bInterval - 1;
+                else
+                        subs->syncinterval = 3;
         }
 
         /* always fill max packet size */