Re: [alsa-devel] [PATCH] [SOUND] recording gain control

Takashi Iwai
2009-03-10T12:17:06Z

At Tue, 10 Mar 2009 10:00:13 +0100,
Clemens Ladisch wrote:
>
> (CC alsa-devel)
>
> Viral Mehta wrote:
> > Hi,
> >
> > I am trying to do gain control while RECORDING for my Audio Mic device.
> >
> > My application opens /dev/mixer device and calls ioctl(fdmixer,
> > MIXER_WRITE(SOUND_MIXER_MIC), ...)
> >
> > But, the call fails. It traces to sound/core/oss/mixer_oss.c file and
> > snd_mixer_oss_put_volume1() function.
> > It never falls in "if (slot->present & SNDRV_MIXER_OSS_PRESENT_CVOLUME)"
> > as condition "if (slot->present & SNDRV_MIXER_OSS_PRESENT_PVOLUME) "
> > comes as false.
> >
> > I think there is a bug in kernel and I think it should be like as below,
> >
> > --- sound/core/oss/mixer_oss.c 2008-12-03 13:24:02.000000000 +0530
> > +++ sound/core/oss/mixer_oss.c 2009-03-09 16:22:06.548766896 +0530
> > @@ -688,7 +688,7 @@ static int snd_mixer_oss_put_volume1(str
> >
> > if (slot->present & SNDRV_MIXER_OSS_PRESENT_PVOLUME) {
> > snd_mixer_oss_put_volume1_vol(fmixer, pslot,
> > slot->numid[SNDRV_MIXER_OSS_ITEM_PVOLUME], left, right);
> > - if (slot->present & SNDRV_MIXER_OSS_PRESENT_CVOLUME)
> > + } else if (slot->present & SNDRV_MIXER_OSS_PRESENT_CVOLUME) {
> > snd_mixer_oss_put_volume1_vol(fmixer, pslot,
> > slot->numid[SNDRV_MIXER_OSS_ITEM_CVOLUME], left, right);
> > } else if (slot->present & SNDRV_MIXER_OSS_PRESENT_GVOLUME) {
> > snd_mixer_oss_put_volume1_vol(fmixer, pslot,
> > slot->numid[SNDRV_MIXER_OSS_ITEM_GVOLUME], left, right);
>
> Your mailer mangled the patch; see linux/Documentation/email-clients.txt.

Also, the current code behaves intentionally so (as it's designed for
mic-loopback volume).

A more feasible fix would be to add another if check for *_CVOLUME
instead of moving it.

Takashi