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ALSA: usb - Avoid unnecessary sample rate changes on USB 2.0 clock sources

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The Scarlett 2i2 seems to take almost 500 ms to set the sample rate,
even if the clock is currently set to that value. This patch speeds
up prepare of the device, by avoiding setting the clock to something
it already is.

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
David Henningsson 2013-04-25 14:32:24 +02:00 committed by Takashi Iwai
parent 4b417cf016
commit fa92dd77ec
1 changed files with 2 additions and 0 deletions
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2
sound/usb/clock.c
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@ -356,6 +356,8 @@ static int set_sample_rate_v2(struct snd_usb_audio *chip, int iface,
return clock;
prev_rate = get_sample_rate_v2(chip, iface, fmt->altsetting, clock);
if (prev_rate == rate)
return 0;
cs_desc = snd_usb_find_clock_source(chip->ctrl_intf, clock);
writeable = uac2_control_is_writeable(cs_desc->bmControls, UAC2_CS_CONTROL_SAM_FREQ - 1);