2011/8/18 Takashi Iwai<tiwai at suse.de http://mailman.alsa-project.org/mailman/listinfo/alsa-devel>:

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/ At Tue, 16 Aug 2011 13:31:52 +0100,

/>/ Colin Guthrie wrote: />>/ />>/ > diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c />>/ > index c04d7c7..cdd19d7 100644 />>/ > --- a/sound/usb/mixer.c />>/ > +++ b/sound/usb/mixer.c />>/ > @@ -152,6 +152,7 @@ static inline void check_mapped_dB(const struct usbmix_name_map *p, />>/ > if (p&& p->dB) { />>/ > cval->dBmin = p->dB->min; />>/ > cval->dBmax = p->dB->max; />>/ > + cval->initialized = 1; />>/ > } />>/ > } />>/ > />>/ > @@ -1092,7 +1093,7 @@ static void build_feature_ctl(struct mixer_build *state, void *raw_desc, />>/ > " Switch" : " Volume"); />>/ > if (control == UAC_FU_VOLUME) { />>/ > check_mapped_dB(map, cval); />>/ > - if (cval->dBmin< cval->dBmax) { />>/ > + if (cval->dBmin< cval->dBmax || !cval->initialized) { />>/ > kctl->tlv.c = mixer_vol_tlv; />>/ > kctl->vd[0].access |= />>/ > SNDRV_CTL_ELEM_ACCESS_TLV_READ | />>/ />>/ />>/ />>/ Not had a chance to test this yet but I will when I get a moment. />/ />/ Any chance to test the patch? />/ / The patch seem fix the no dB scale problem , however the broken dB test which you added seem redundant as cval->dBmin and cval->dBmax are still zero because error in get_min_max() at build_feature_ctl() and it seem that the valid dBmin and dBMax are calculated by get_min_max() at mixer_ctl_feature_info() on my usb logitech web cam

LSA endpoint.c:450: 2:3:1: add audio endpoint 0x86 ALSA mixer.c:1182: [5] FU [Mic Capture Switch] ch = 1, val = 0/1/1 ALSA mixer.c:804: 5:2: cannot get min/max values for control 2 (id 5) ALSA mixer.c:1182: [5] FU [Mic Capture Volume] ch = 1, val = 0/1/1 ALSA mixer.c:804: 5:2: cannot get min/max values for control 2 (id 5) usbcore: registered new interface driver snd-usb-audio

Fixed dB scale problem for my USB Logitech headset as well (046d:0a0b)