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| author | Daniel Mack <daniel@caiaq.de> | 2010-06-16 17:57:30 +0200 |
|---|---|---|
| committer | Takashi Iwai <tiwai@suse.de> | 2010-06-23 16:09:50 +0200 |
| commit | 157a57b6fae7d3c6d24b7623dcc6679c6d244621 (patch) | |
| tree | d4e803455aa7cbcab244355171be428a3b33fa47 /sound/usb/clock.c | |
| parent | 21af7d8c0c0a88f6f9fc6993d73001b4caf23b08 (diff) | |
| download | linux-157a57b6fae7d3c6d24b7623dcc6679c6d244621.tar.bz2 | |
ALSA: usb-audio: move and add some comments
Also add a list of open topics.
Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound/usb/clock.c')
| -rw-r--r-- | sound/usb/clock.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/sound/usb/clock.c b/sound/usb/clock.c index 386b09c5ce73..7279d6190875 100644 --- a/sound/usb/clock.c +++ b/sound/usb/clock.c @@ -120,8 +120,6 @@ static bool uac_clock_source_is_valid(struct snd_usb_audio *chip, int source_id) return !!data; } -/* Try to find the clock source ID of a given clock entity */ - static int __uac_clock_find_source(struct snd_usb_audio *chip, struct usb_host_interface *host_iface, int entity_id, unsigned long *visited) @@ -154,6 +152,8 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip, if (ret < 0) return ret; + /* Selector values are one-based */ + if (ret > selector->bNrInPins || ret < 1) { printk(KERN_ERR "%s(): selector reported illegal value, id %d, ret %d\n", @@ -176,6 +176,17 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip, return -EINVAL; } +/* + * For all kinds of sample rate settings and other device queries, + * the clock source (end-leaf) must be used. However, clock selectors, + * clock multipliers and sample rate converters may be specified as + * clock source input to terminal. This functions walks the clock path + * to its end and tries to find the source. + * + * The 'visited' bitfield is used internally to detect recursive loops. + * + * Returns the clock source UnitID (>=0) on success, or an error. + */ int snd_usb_clock_find_source(struct snd_usb_audio *chip, struct usb_host_interface *host_iface, int entity_id) @@ -246,6 +257,7 @@ static int set_sample_rate_v2(struct snd_usb_audio *chip, int iface, return clock; if (!uac_clock_source_is_valid(chip, clock)) { + /* TODO: should we try to find valid clock setups by ourself? */ snd_printk(KERN_ERR "%d:%d:%d: clock source %d is not valid, cannot use\n", dev->devnum, iface, fmt->altsetting, clock); return -ENXIO; |