ALSA: usb-audio: Add mute TLV for playback volumes on C-Media devices

commit 0f174b3525a43bd51f9397394763925e0ebe7bc7 upstream.

C-Media devices (at least some models) mute the playback stream when
volumes are set to the minimum value.  But this isn't informed via TLV
and the user-space, typically PulseAudio, gets confused as if it's
still played in a low volume.

This patch adds the new flag, min_mute, to struct usb_mixer_elem_info
for indicating that the mixer element is with the minimum-mute volume.
This flag is set for known C-Media devices in
snd_usb_mixer_fu_apply_quirk() in turn.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=196669
Signed-off-by: Takashi Iwai <tiwai@suse.de>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 9c36a1f..b6bef94 100644 (file)
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -515,6 +515,8 @@ static int mixer_vol_tlv(struct snd_kcontrol *kcontrol, int op_flag,
 
        if (size < sizeof(scale))
                return -ENOMEM;
+       if (cval->min_mute)
+               scale[0] = SNDRV_CTL_TLVT_DB_MINMAX_MUTE;
        scale[2] = cval->dBmin;
        scale[3] = cval->dBmax;
        if (copy_to_user(_tlv, scale, sizeof(scale)))

diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
index 81b2d8a..355c5e1 100644 (file)
--- a/sound/usb/mixer.h
+++ b/sound/usb/mixer.h
@@ -52,6 +52,7 @@ struct usb_mixer_elem_info {
        int cached;
        int cache_val[MAX_CHANNELS];
        u8 initialized;
+       u8 min_mute;
 };
 
 int snd_usb_create_mixer(struct snd_usb_audio *chip, int ctrlif,

diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index d422d16..ee1a148 100644 (file)
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -726,6 +726,12 @@ void snd_usb_mixer_fu_apply_quirk(struct usb_mixer_interface *mixer,
                if (unitid == 7 && cval->control == UAC_FU_VOLUME)
                        snd_dragonfly_quirk_db_scale(mixer, cval, kctl);
                break;
+       /* lowest playback value is muted on C-Media devices */
+       case USB_ID(0x0d8c, 0x000c):
+       case USB_ID(0x0d8c, 0x0014):
+               if (strstr(kctl->id.name, "Playback"))
+                       cval->min_mute = 1;
+               break;
        }
 }