ALSA: usb-audio: clean up find_audio_control_unit()

Use a struct to parse the audio units, and return usable descriptors
for all types. There's no need to limit the result set, except for some
kind of sanity check.

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

1 files changed, 10 insertions, 8 deletions

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 8be6bf2552b..cb345360f81 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -165,22 +165,24 @@ static int check_mapped_selector_name(struct mixer_build *state, int unitid,
 
 /*
  * find an audio control unit with the given unit id
- * this doesn't return any clock related units, so they need to be handled elsewhere
  */
 static void *find_audio_control_unit(struct mixer_build *state, unsigned char unit)
 {
-        unsigned char *p;
+        /* we just parse the header */
+        struct uac_feature_unit_descriptor *hdr = NULL;
 
-        p = NULL;
-        while ((p = snd_usb_find_desc(state->buffer, state->buflen, p,
-                                      USB_DT_CS_INTERFACE)) != NULL) {
-                if (p[0] >= 4 && p[2] >= UAC_INPUT_TERMINAL && p[2] <= UAC2_EXTENSION_UNIT_V2 && p[3] == unit)
-                        return p;
+        while ((hdr = snd_usb_find_desc(state->buffer, state->buflen, hdr,
+                                        USB_DT_CS_INTERFACE)) != NULL) {
+                if (hdr->bLength >= 4 &&
+                    hdr->bDescriptorSubtype >= UAC_INPUT_TERMINAL &&
+                    hdr->bDescriptorSubtype <= UAC2_SAMPLE_RATE_CONVERTER &&
+                    hdr->bUnitID == unit)
+                        return hdr;
         }
+
         return NULL;
 }
 
-
 /*
  * copy a string with the given id
  */