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| author | Clemens Ladisch <clemens@ladisch.de> | 2005-08-12 10:28:27 +0400 |
|---|---|---|
| committer | Jaroslav Kysela <perex@suse.cz> | 2005-08-30 10:45:08 +0400 |
| commit | d6db392e9235c48bb945624798e9beede7b85b12 (patch) | |
| tree | 5f17b000a18f476ea296b1387150b7ff92837215 | |
| parent | 15a24c0778e9bdd48d8e1cf60a263837b5c30ed5 (diff) | |
| download | linux-d6db392e9235c48bb945624798e9beede7b85b12.tar.xz | |
[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.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c index 9e38d3d1322a..d28106e390c4 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 { |