[PATCH 3.16 119/294] ALSA: usb-audio: Add mute TLV for playback volumes on C-Media devices

From: Ben Hutchings
Date: Mon Nov 06 2017 - 19:27:09 EST


3.16.50-rc1 review patch. If anyone has any objections, please let me know.

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

From: Takashi Iwai <tiwai@xxxxxxx>

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@xxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
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
@@ -533,6 +533,8 @@ 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
@@ -53,6 +53,7 @@ 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,
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -1759,6 +1759,12 @@ 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;
}
}