[alsa-devel] On mixer controls naming

Hi,

I'm trying to write a new driver for a virtual sound card. It isn't actually a sound card, but only a software solution to control volume and bass of an external device (using SPI and GPIO). So it only has a mixer (no pcm or capture subdevices).

I could successfully configure two controls "Master Playback Switch" and "Master Playback Volume". Alsamixer shows them correctly under "Playback" view (and very nicely it joined them together to form a single composite control "Master")

The other control I've named "Tone Control - Bass", as indicated in writing-an-alsa-driver.pdf. But alsamixer shows it under both "Playback" and "Capture" views.

How can I restrict this latter control to just playback?