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Commit d6db392e authored by Clemens Ladisch's avatar Clemens Ladisch Committed by Jaroslav Kysela
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[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: default avatarClemens Ladisch <clemens@ladisch.de>
parent 15a24c07

sound/usb/usbaudio.c

+9 −1
Original line number Diff line number Diff line
@@ -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 {