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Subject[PATCH 4.4 09/20] ALSA: usb-audio: Add mute TLV for playback volumes on C-Media devices
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@suse.de>

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
sound/usb/mixer.c | 2 ++
sound/usb/mixer.h | 1 +
sound/usb/mixer_quirks.c | 6 ++++++
3 files changed, 9 insertions(+)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -541,6 +541,8 @@ int snd_usb_mixer_vol_tlv(struct snd_kco

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)))
--- a/sound/usb/mixer.h
+++ b/sound/usb/mixer.h
@@ -64,6 +64,7 @@ struct usb_mixer_elem_info {
int cached;
int cache_val[MAX_CHANNELS];
u8 initialized;
+ u8 min_mute;
void *private_data;
};

--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -1873,6 +1873,12 @@ void snd_usb_mixer_fu_apply_quirk(struct
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;
}
}


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