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Commit 15a24c07 authored by Clemens Ladisch's avatar Clemens Ladisch Committed by Jaroslav Kysela
Browse files

[ALSA] usb-audio: use 1 ms URBs when capturing 



USB generic driver
When capturing audio data, we do not know beforehand how many samples
the device sends per frame, so we have to use URBs that are as short as
possible to make sure that we can handle period boundaries without any
additional latencies.

Furthermore, the total count of URBs submitted doesn't matter when
capturing, so we can just use the maximum number.

Signed-off-by: default avatarClemens Ladisch <clemens@ladisch.de>
parent a53fc188

sound/usb/usbaudio.c

+12 −6
Original line number Diff line number Diff line
@@ -97,7 +97,7 @@ MODULE_PARM_DESC(async_unlink, "Use async unlink mode."); 


#define MAX_PACKS	10

#define MAX_PACKS_HS	(MAX_PACKS * 8)	/* in high speed mode */

#define MAX_URBS	5	/* max. 20ms long packets */

#define MAX_URBS	8

#define SYNC_URBS	4	/* always four urbs for sync */

#define MIN_PACKS_URB	1	/* minimum 1 packet per urb */
@@ -920,10 +920,12 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by 
	else

		subs->curpacksize = maxsize;



	if (snd_usb_get_speed(subs->dev) == USB_SPEED_FULL)

	if (is_playback)

		urb_packs = nrpacks;

	else

		urb_packs = (nrpacks * 8) >> subs->datainterval;

		urb_packs = 1;

	if (snd_usb_get_speed(subs->dev) == USB_SPEED_HIGH)

		urb_packs = (urb_packs * 8) >> subs->datainterval;



	/* allocate a temporary buffer for playback */

	if (is_playback) {
@@ -935,9 +937,13 @@ 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;

		if (total_packs < 2 * MIN_PACKS_URB)

			total_packs = 2 * MIN_PACKS_URB;

	} else {

		total_packs = MAX_URBS * urb_packs;

	}

	subs->nurbs = (total_packs + urb_packs - 1) / urb_packs;

	if (subs->nurbs > MAX_URBS) {

		/* too much... */