ALSA: usb: use multiple packets per urb for Wireless USB inbound audio

For Wireless USB audio devices, use multiple isoc packets per URB for
inbound endpoints with a datainterval < 5.  This allows the WUSB host
controller to take advantage of bursting to service endpoints whose
logical polling interval is less than the 4ms minimum polling interval
limit in WUSB.

Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index b9ba0fcc45df10d4151bb39f8a5d6284dc8ec23e..83aabea259d7113d82d94d870bd04ebffd64b633 100644 (file)
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -636,8 +636,22 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep,
        if (usb_pipein(ep->pipe) ||
                        snd_usb_endpoint_implicit_feedback_sink(ep)) {
 
+               urb_packs = packs_per_ms;
+               /*
+                * Wireless devices can poll at a max rate of once per 4ms.
+                * For dataintervals less than 5, increase the packet count to
+                * allow the host controller to use bursting to fill in the
+                * gaps.
+                */
+               if (snd_usb_get_speed(ep->chip->dev) == USB_SPEED_WIRELESS) {
+                       int interval = ep->datainterval;
+                       while (interval < 5) {
+                               urb_packs <<= 1;
+                               ++interval;
+                       }
+               }
                /* make capture URBs <= 1 ms and smaller than a period */
-               urb_packs = min(max_packs_per_urb, packs_per_ms);
+               urb_packs = min(max_packs_per_urb, urb_packs);
                while (urb_packs > 1 && urb_packs * maxsize >= period_bytes)
                        urb_packs >>= 1;
                ep->nurbs = MAX_URBS;