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

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Date:	Tue, 10 Mar 2009 13:16:50 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	Viral Mehta <viral.mehta@...fochips.com>,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [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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