ALSA: usb-audio - Don't expose broken dB ranges
Some crappy USB-audio devices give broken dB ranges, e.g. both min and max
are 0dB. This confuses the volume control that prefers dB expression such
as alsactl or PulseAudio. In such a case, it's much better not to expose
the broken dB information.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 5e47757..c8c28cd 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1097,11 +1097,13 @@
append_ctl_name(kctl, control == UAC_FU_MUTE ?
" Switch" : " Volume");
if (control == UAC_FU_VOLUME) {
- kctl->tlv.c = mixer_vol_tlv;
- kctl->vd[0].access |=
- SNDRV_CTL_ELEM_ACCESS_TLV_READ |
- SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK;
check_mapped_dB(map, cval);
+ if (cval->dBmin < cval->dBmax) {
+ kctl->tlv.c = mixer_vol_tlv;
+ kctl->vd[0].access |=
+ SNDRV_CTL_ELEM_ACCESS_TLV_READ |
+ SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK;
+ }
}
break;