From mboxrd@z Thu Jan  1 00:00:00 1970
From: Takashi Iwai <tiwai@suse.de>
Subject: Re: ALSA: hda: hdmi: Hint matching between
	input	devices and pcm devices
Date: Mon, 12 Sep 2011 09:10:58 +0200
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To: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Cc: alsa-devel@alsa-project.org, 'Clemens Ladisch' <clemens@ladisch.de>
List-Id: alsa-devel@alsa-project.org

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