At Tue, 30 Aug 2011 08:01:50 -0500, Pierre-Louis Bossart wrote:

Hi Clemens,

...

If the driver can detect ELD changes, it must inform userspace that the control has changed. If there is no ELD, the _get callback should return an error, and the control should have been set to unreadable.

Bear with my ignorance of controls, but how does the driver 'inform userspace that the control has changed'?

The control API has a notification mechanism. You can find some drivers calling snd_ctl_notify().

Takashi