sound: usb-audio: do not make URBs longer than sync packet interval

Using more packets in one URB do avoid interrupts does not make sense
when we have a sync pipe whose packets generate interrupts more often.
Therefore, limit the URB size to the synchronization packet interval.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 44b9cdc8a83bae15856ca18fb7915acc7197757d..fa3f7a1dc5e1669baeca955d64bb0019f23c8920 100644 (file)
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -1083,6 +1083,8 @@ static int init_substream_urbs(struct snd_usb_substream *subs, unsigned int peri
        } else
                urb_packs = 1;
        urb_packs *= packs_per_ms;
+       if (subs->syncpipe)
+               urb_packs = min(urb_packs, 1 << subs->syncinterval);
 
        /* decide how many packets to be used */
        if (is_playback) {