ALSA: usb-audio: parse clock topology of UAC2 devices

Audio devices which comply to the UAC2 standard can export complex clock
topologies in its descriptors and set up links between them.

The entities that are defined are

 - clock sources, which define the end-leafs.
 - clock selectors, which act as switch to select one out of many
   possible clocks sources.
 - clock multipliers, which have an input clock source, and act as clock
   source again. They can be used to derive one clock from another.

All sample rate changes, clock validity queries and the like must go to
clock source elements, while clock selectors and multipliers can be used
as terminal clock source.

The following patch adds a parser for these elements and functions to
iterate over the tree and find the leaf nodes (clock sources).

The samplerate set functions were moved to the new clock.c file.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 2 insertions, 16 deletions

diff --git a/sound/usb/card.c b/sound/usb/card.c
index da1346bd485..7a8ac1d81be 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -236,7 +236,6 @@ static int snd_usb_create_streams(struct snd_usb_audio *chip, int ctrlif)
         }
 
         case UAC_VERSION_2: {
-                struct uac_clock_source_descriptor *cs;
                 struct usb_interface_assoc_descriptor *assoc =
                         usb_ifnum_to_if(dev, ctrlif)->intf_assoc;
 
@@ -245,21 +244,6 @@ static int snd_usb_create_streams(struct snd_usb_audio *chip, int ctrlif)
                         return -EINVAL;
                 }
 
-                /* FIXME: for now, we expect there is at least one clock source
-                 * descriptor and we always take the first one.
-                 * We should properly support devices with multiple clock sources,
-                 * clock selectors and sample rate conversion units. */
-
-                cs = snd_usb_find_csint_desc(host_iface->extra, host_iface->extralen,
-                                                NULL, UAC2_CLOCK_SOURCE);
-
-                if (!cs) {
-                        snd_printk(KERN_ERR "CLOCK_SOURCE descriptor not found\n");
-                        return -EINVAL;
-                }
-
-                chip->clock_id = cs->bClockID;
-
                 for (i = 0; i < assoc->bInterfaceCount; i++) {
                         int intf = assoc->bFirstInterface + i;
 
@@ -481,6 +465,8 @@ static void *snd_usb_audio_probe(struct usb_device *dev,
                         goto __error;
         }
 
+        chip->ctrl_intf = alts;
+
         if (err > 0) {
                 /* create normal USB audio interfaces */
                 if (snd_usb_create_streams(chip, ifnum) < 0 ||