Hello,

Thanks for your help.

...

What ioctl request code would I have to pass in order to reach this control's put/get methods?

snd_ctl_elem_write() (alsa-lib/src/control/control.c) snd_ctl_hw_elem_write() (alsa-lib/src/control/control_hw.c) ioctl(SNDRV_CTL_IOCTL_ELEM_WRITE) snd_ctl_ioctl() (linux/sound/core/control.c) snd_ctl_elem_write_user() snd_ctl_elem_write() kctl->put()

This is the path in the alsa world. I have followed this code as well, and it uses the alsa control element as payload into the ioctl.

I have taken a more pragmatic and certainly less orthodox one:

ioctl(mixerFd, SOUND_MIXER_WRITE_VOLUME, &leftright);

will eventually call the put method of a kernel control pmic_control_pb_vol with the name "Master Playback Volume".

The function snd_mixer_oss_build_input() appears to be responsible for creating this link, by looking through a list of words such as "Master", "CD", etc in conjunction with expressions such as "%s Playback Volume". It probably will then try to match the names of the alsa kernel controls and set the put function pointer if appropriate.

Consequently, if I rename the control responsible for the output, pmic_control_op_sw, to something for which a ioctl exists, e.g. "CD", then it works as a pseudo volume control and I can use:

ioctl(mixerFd, SOUND_MIXER_WRITE_CD, &output);

This approach is admittedly a hack, but it works. This ioctl will result in the call of the fake CD control and its put method.

If I had renamed the the output control "Master Output Switch", I could not have used a volume control and hence I would not know what ioctl request code to use.

Regards, peter