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authorDaniel Mack <daniel@caiaq.de>2010-06-16 17:57:30 +0200
committerTakashi Iwai <tiwai@suse.de>2010-06-23 16:09:50 +0200
commit157a57b6fae7d3c6d24b7623dcc6679c6d244621 (patch)
treed4e803455aa7cbcab244355171be428a3b33fa47 /sound/usb/clock.c
parent21af7d8c0c0a88f6f9fc6993d73001b4caf23b08 (diff)
downloadop-kernel-dev-157a57b6fae7d3c6d24b7623dcc6679c6d244621.zip
op-kernel-dev-157a57b6fae7d3c6d24b7623dcc6679c6d244621.tar.gz
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.c16
1 files changed, 14 insertions, 2 deletions
diff --git a/sound/usb/clock.c b/sound/usb/clock.c
index 386b09c..7279d61 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;
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