[alsa-devel] [PATCH 2/3] ASoC: wm_adsp: Add support for grouped ALSA binary controls

Dimitris Papastamos dp at opensource.wolfsonmicro.com
Fri Nov 1 11:46:27 CET 2013

On Thu, Oct 31, 2013 at 08:55:53AM +0100, Takashi Iwai wrote:
> At Wed, 30 Oct 2013 16:54:29 +0000,
> Dimitris Papastamos wrote:
> > 
> > Currently the ALSA ABI imposes a hard limit of 512 bytes per binary
> > control.  To support coefficient data blocks of larger sizes we carve up
> > this space into multiple alsa controls.  All of these controls are
> > identified by a common prefix and suffix of the form ":<blk id>".
> > 
> > Control groupings can also consist of a single block in which case the
> > suffix ":0" is used.
> Why not using the control element index?
> You can create each kctl element individually with a different index,
> but also you can create multiple ctl elements in a single shot by
> passing to snd_kcontrol_new.count field.  This will create a grouped 
> object, thus it saves spaces, too, in comparison with individual
> kctls.  The drawback is that you need to retrieve the real index via
> snd_ctl_get_ioff*() in each control callback.

I will give this a shot when I have some time and re-send the patch.


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