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


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