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[ALSA] usb-audio: schedule high speed URBs with 1 ms alignment 

USB generic driver
The EHCI driver doesn't interrupt more than once per millisecond, and
organizes all iso transfers with frame-sized ITDs, so we can (try to)
be more efficient by aligning all URBs on frame boundaries.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
This commit is contained in:
Clemens Ladisch 2005-08-12 15:19:39 +02:00 коммит произвёл Jaroslav Kysela
Родитель 71d848ca00
Коммит a93bf99077
1 изменённых файлов: 14 добавлений и 6 удалений
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20
sound/usb/usbaudio.c
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@ -893,7 +893,7 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
{
unsigned int maxsize, n, i;
int is_playback = subs->direction == SNDRV_PCM_STREAM_PLAYBACK;
unsigned int npacks[MAX_URBS], urb_packs, total_packs;
unsigned int npacks[MAX_URBS], urb_packs, total_packs, packs_per_ms;
/* calculate the frequency in 16.16 format */
if (snd_usb_get_speed(subs->dev) == USB_SPEED_FULL)
@ -920,14 +920,18 @@ 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_HIGH)
packs_per_ms = 8 >> subs->datainterval;
else
packs_per_ms = 1;
if (is_playback) {
urb_packs = nrpacks;
urb_packs = max(urb_packs, (unsigned int)MIN_PACKS_URB);
urb_packs = min(urb_packs, (unsigned int)MAX_PACKS);
} else
urb_packs = 1;
if (snd_usb_get_speed(subs->dev) == USB_SPEED_HIGH)
urb_packs = (urb_packs * 8) >> subs->datainterval;
urb_packs *= packs_per_ms;
/* allocate a temporary buffer for playback */
if (is_playback) {
@ -949,8 +953,12 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
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;
/* round up to multiple of packs_per_ms */
total_packs = (total_packs + packs_per_ms - 1)
& ~(packs_per_ms - 1);
/* we need at least two URBs for queueing */
if (total_packs < 2 * MIN_PACKS_URB * packs_per_ms)
total_packs = 2 * MIN_PACKS_URB * packs_per_ms;
} else {
total_packs = MAX_URBS * urb_packs;
}
@ -972,7 +980,7 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
subs->nurbs = 2;
npacks[0] = (total_packs + 1) / 2;
npacks[1] = total_packs - npacks[0];
} else if (npacks[subs->nurbs-1] < MIN_PACKS_URB) {
} else if (npacks[subs->nurbs-1] < MIN_PACKS_URB * packs_per_ms) {
/* the last packet is too small.. */
if (subs->nurbs > 2) {
/* merge to the first one */