linux-kernel - Re: [alsa-devel] [PATCH] ASoC: dpcm: don't do hw_param when BE has done hw

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Date:	Mon, 13 Jan 2014 10:48:51 +0000
From:	Liam Girdwood <liam.r.girdwood@...ux.intel.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	Mark Brown <broonie@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Nenghua Cao <nhcao@...vell.com>
Subject: Re: [alsa-devel] [PATCH] ASoC: dpcm: don't do hw_param when BE has
 done	hw_param

On Sat, 2014-01-11 at 10:35 +0100, Takashi Iwai wrote:
> At Fri, 10 Jan 2014 18:43:09 +0000,
> Liam Girdwood wrote:
> > 
> > On Fri, 2014-01-10 at 14:46 +0100, Takashi Iwai wrote:
> > > At Fri, 10 Jan 2014 12:29:08 +0000,
> > > Liam Girdwood wrote:
> > > > 

> > 
> > The intention was to use the existing alsa-lib/tinyalsa PCM hw_params
> > APIs. The BE would just export itself to usespace as a PCM (but without
> > the capability for direct playback/capture - just format, rate setting)
> 
> Does it mean that, from kernel perspective, a BE creates a dedicated
> (virtual) PCM device and expose it to user-space?  Or just through
> special API?

I'm thinking a virtual PCM if you agree. 

We could keep the same userspace API for configuration OR we could
extend the API slightly to add some snd_pcm_virtual_() functions.
Extending the API would imply the virtual PCM only supports a subset of
PCM API calls (avoiding any confusion/mixing with regular PCM APIs).

Thanks

Liam    


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