[alsa-devel] Why analog loopback of sigmatel devices got removed?

Takashi Iwai tiwai at suse.de
Fri Jun 19 08:32:37 CEST 2009

At Fri, 19 Jun 2009 02:50:35 +0300,
Maxim Levitsky wrote:
> Hi,
> Due to lack of time, I didn't update kernel on my desktop system.
> Now I notice that analog loopback go removed. Why?

Because it harms than helps more often.  I've got tons of bug reports
and been upset just because users blindly set "Analog Loopback" mixer
switch and lost their sound output.  This is no mixer element that
behaves intuitively -- it shuts out PCM output instead of adding the
analog loopback like other hardwares.

The feature is still available, though.  You just need to give the
driver an instruction via sysfs.  Namely, write to sysfs files
corresponding to the IDT codec like
	# echo "loopback yes" > /sys/class/sound/hwC0D0/hints
	# echo 1 > /sys/class/sound/hwC0D0/reconfig
Then the driver will reconfigure with the loopback mixer element.
I have a patch series to add this with a "patch" firmware file to
make it easier, which I'm going to send an RFC to this ML soon later.
Take a look at topic/hda-patch branch on sound-unstable tree.



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