[alsa-devel] ioctl request code for specific alsa control

Clemens Ladisch clemens at ladisch.de
Wed May 14 11:17:02 CEST 2008

Peter Wurmsdobler wrote:
> ...
> Another control is called pmic_control_op_sw (.name = "Master Output
> Playback Volume") and appears in amixer as "Master Output" (in fact it
> is not a volume control but a switch).

Then I'd guess its name should be "Master Playback Switch".
See Documentation/sound/alsa/ControlNames.txt.

> What is the ioctl request code for a particular snd_kcontrol_new_t
> defined in the driver?

ALSA controls do not have separate ioctl codes.  Controls are identified
by their name (or by their ID, which is a number that ALSA assigns
automatically).  There is one ioctl request that writes the value of a
control and which gets the control ID as parameter.

> Alternatively, how does the OSS layer in ALSA map the different ALSA
> controls to the predefined and fixed OSS controls?

The OSS API has some predefined mixer controls that are identifed by a
number or ioctl request.  By default, ALSA maps these OSS controls to
certain ALSA control names; see section "Mixer Elements" in


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