[ALSA] usb-audio - use proper interval between synchronization packets

USB generic driver
Add sanity checks when reading the bRefresh value, and actually use it
for the synchronization packets instead of polling at 1000 Hz.

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

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index e759b73942c257c260752bbeabce05a09d45b6ee..e1a648d7ffff882e7fa7d5115f97c5361cba249b 100644 (file)
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -1051,10 +1051,7 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
                        u->urb->pipe = subs->syncpipe;
                        u->urb->transfer_flags = URB_ISO_ASAP;
                        u->urb->number_of_packets = u->packets;
-                       if (snd_usb_get_speed(subs->dev) == USB_SPEED_HIGH)
-                               u->urb->interval = 8;
-                       else
-                               u->urb->interval = 1;
+                       u->urb->interval = 1 << subs->syncinterval;
                        u->urb->context = u;
                        u->urb->complete = snd_usb_complete_callback(snd_complete_sync_urb);
                }
@@ -1272,7 +1269,12 @@ static int set_format(snd_usb_substream_t *subs, struct audioformat *fmt)
                        subs->syncpipe = usb_rcvisocpipe(dev, ep);
                else
                        subs->syncpipe = usb_sndisocpipe(dev, ep);
-               subs->syncinterval = get_endpoint(alts, 1)->bRefresh;
+               if (get_endpoint(alts, 1)->bLength >= USB_DT_ENDPOINT_AUDIO_SIZE &&
+                   get_endpoint(alts, 1)->bRefresh >= 1 &&
+                   get_endpoint(alts, 1)->bRefresh <= 9)
+                       subs->syncinterval = get_endpoint(alts, 1)->bRefresh;
+               else
+                       subs->syncinterval = 1;
        }
 
        /* always fill max packet size */