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>

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 43d6417..9149a84 100644 (file)
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -462,6 +462,16 @@ static int set_cur_mix_value(struct usb_mixer_elem_info *cval, int channel,
                             int index, int value)
 {
        int err;
+       unsigned int read_only = (channel == 0) ?
+               cval->master_readonly :
+               cval->ch_readonly & (1 << (channel - 1));
+
+       if (read_only) {
+               snd_printdd(KERN_INFO "%s(): channel %d of control %d is read_only\n",
+                           __func__, channel, cval->control);
+               return 0;
+       }
+
        err = snd_usb_mixer_set_ctl_value(cval, UAC_SET_CUR, (cval->control << 8) | channel,
                            value);
        if (err < 0)
@@ -958,7 +968,7 @@ static size_t append_ctl_name(struct snd_kcontrol *kctl, const char *str)
 static void build_feature_ctl(struct mixer_build *state, void *raw_desc,
                              unsigned int ctl_mask, int control,
                              struct usb_audio_term *iterm, int unitid,
-                             int read_only)
+                             int readonly_mask)
 {
        struct uac_feature_unit_descriptor *desc = raw_desc;
        unsigned int len = 0;
@@ -989,20 +999,25 @@ static void build_feature_ctl(struct mixer_build *state, void *raw_desc,
        cval->control = control;
        cval->cmask = ctl_mask;
        cval->val_type = audio_feature_info[control-1].type;
-       if (ctl_mask == 0)
+       if (ctl_mask == 0) {
                cval->channels = 1;     /* master channel */
-       else {
+               cval->master_readonly = readonly_mask;
+       } else {
                int i, c = 0;
                for (i = 0; i < 16; i++)
                        if (ctl_mask & (1 << i))
                                c++;
                cval->channels = c;
+               cval->ch_readonly = readonly_mask;
        }
 
        /* get min/max values */
        get_min_max(cval, 0);
 
-       if (read_only)
+       /* if all channels in the mask are marked read-only, make the control
+        * read-only. set_cur_mix_value() will check the mask again and won't
+        * issue write commands to read-only channels. */
+       if (cval->channels == readonly_mask)
                kctl = snd_ctl_new1(&usb_feature_unit_ctl_ro, cval);
        else
                kctl = snd_ctl_new1(&usb_feature_unit_ctl, cval);
@@ -1195,9 +1210,12 @@ static int parse_audio_feature_unit(struct mixer_build *state, int unitid, void
                                }
                        }
 
-                       /* FIXME: the whole unit is read-only if any of the channels is marked read-only */
+                       /* NOTE: build_feature_ctl() will mark the control read-only if all channels
+                        * are marked read-only in the descriptors. Otherwise, the control will be
+                        * reported as writeable, but the driver will not actually issue a write
+                        * command for read-only channels */
                        if (ch_bits & 1) /* the first channel must be set (for ease of programming) */
-                               build_feature_ctl(state, _ftr, ch_bits, i, &iterm, unitid, !!ch_read_only);
+                               build_feature_ctl(state, _ftr, ch_bits, i, &iterm, unitid, ch_read_only);
                        if (uac2_control_is_readable(master_bits, i))
                                build_feature_ctl(state, _ftr, 0, i, &iterm, unitid,
                                                  !uac2_control_is_writeable(master_bits, i));

diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
index 1301238..a7cf100 100644 (file)
--- 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;