[alsa-devel] usb-audio: Correct way to do a mixer quirk?

[Mark Hills]

The Electrix Ebox-44 is a new USB interface, but the MIXER_UNIT descriptor 
is broken and refers to a non-existing unit_id.

I worked around it with the patch below to remove the additional entry, 
and the device seems to work as expected.

But inserting code here is probably not desirable -- I imagine I need to 
turn this into a quirk of some sort. Am I correct?

And what is the best way to do this?

* It doesn't appear I can use quirks-table.h to adjust the content
  of a mixer unit (the bNrInPins attribute)

* It seems that to use mixer_quirks.c would require a function to
  create the whole mixer

It's possible I'm incorrect on the above, though. Can anyone advise on how 
to make this fix in the correct way?

Many thanks

-- 
Mark


--- 
 AudioControl Interface Descriptor:
    bLength                15
    bDescriptorType        36
    bDescriptorSubtype      4 (MIXER_UNIT)
    bUnitID                 6
    bNrInPins               3         <-- should be 2
    baSourceID( 0)          5
    baSourceID( 1)          4
    baSourceID( 2)          2         <-- bogus entry

---
 sound/usb/mixer.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 8147ffc..ab3ccca 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1387,6 +1387,9 @@ static int parse_audio_mixer_unit(struct mixer_build *state, int unitid, void *r
 		return 0;
 	}
 
+	if (state->chip->usb_id == USB_ID(0x200c, 0x1018) && unitid == 6)
+		input_pins = 2;
+
 	num_ins = 0;
 	ich = 0;
 	for (pin = 0; pin < input_pins; pin++) {
-- 
1.7.4.4