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authorClemens Ladisch <clemens@ladisch.de>2005-08-12 08:28:27 +0200
committerJaroslav Kysela <perex@suse.cz>2005-08-30 08:45:08 +0200
commitd6db392e9235c48bb945624798e9beede7b85b12 (patch)
tree5f17b000a18f476ea296b1387150b7ff92837215
parent15a24c0778e9bdd48d8e1cf60a263837b5c30ed5 (diff)
[ALSA] usb-audio: fix packets per URB calculation for playback
USB generic driver When determining how many packets are needed for one period, we cannot assume that all packets have their maximum size -- we always use the nominal sample rate when sending data, and could use an even lower rate when the endpoint uses frequency feedback. Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
-rw-r--r--sound/usb/usbaudio.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 9e38d3d1322..d28106e390c 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -938,7 +938,15 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
/* decide how many packets to be used */
if (is_playback) {
- total_packs = (period_bytes + maxsize - 1) / maxsize;
+ unsigned int minsize;
+ /* determine how small a packet can be */
+ minsize = (subs->freqn >> (16 - subs->datainterval))
+ * (frame_bits >> 3);
+ /* with sync from device, assume it can be 25% lower */
+ if (subs->syncpipe)
+ minsize -= minsize >> 2;
+ minsize = max(minsize, 1u);
+ total_packs = (period_bytes + minsize - 1) / minsize;
if (total_packs < 2 * MIN_PACKS_URB)
total_packs = 2 * MIN_PACKS_URB;
} else {