ALSA: usb-audio: support partially write-protected UAC2 controls

So far, UAC2 controls are marked read-only if any of the channels are
marked read-only in the descriptors. Change this behaviour and

 - mark them writeable unless all channels are read-only
 - store the read-only mask in usb_mixer_elem_info and
 - check the mask again in set_cur_mix_value(), and bail out for
   write-protected channels.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
index 130123854a6c..a7cf1007fbb0 100644
--- a/sound/usb/mixer.h
+++ b/sound/usb/mixer.h
@@ -34,6 +34,8 @@ struct usb_mixer_elem_info {
         unsigned int id;
         unsigned int control;   /* CS or ICN (high byte) */
         unsigned int cmask; /* channel mask bitmap: 0 = master */
+        unsigned int ch_readonly;
+        unsigned int master_readonly;
         int channels;
         int val_type;
         int min, max, res;