[alsa-devel] [PATCH 2/3] ASoC: Blackfin: add multi-channel supporting in Blackfin ASoC driver and AD1980 codec driver

[Takashi Iwai]

At Tue, 21 Oct 2008 17:35:49 +0800,
Cai, Cliff wrote:
> 
>  
> 
> >-----Original Message-----
> >From: Mark Brown [mailto:broonie at sirena.org.uk] 
> >Sent: Tuesday, October 21, 2008 5:16 PM
> >To: Cai, Cliff
> >Cc: Bryan Wu; alsa-devel at alsa-project.org
> >Subject: Re: [PATCH 2/3] ASoC: Blackfin: add multi-channel 
> >supporting in Blackfin ASoC driver and AD1980 codec driver
> >
> >On Tue, Oct 21, 2008 at 05:08:31PM +0800, Cai, Cliff wrote:
> >
> >> >To be honest, I'm surprised that the multi-channel support 
> >can't only 
> >> >incur the extra memory consumpton when playing back a multi-channel 
> >> >stream - I'd have expected the hardware to work in the same 
> >way for a 
> >> >normal stereo stream even if multi-channel support is built in.
> >
> >> Yes,hardware almost works in the same way as playing a stereo 
> >> stream,except That it need to fill more data to DMA memory 
> >> manually,since we just simulate AC97 Controller using serial port.
> >
> >My point is that the configuration of the hardware for 
> >multi-channel playback only needs to be done when actually 
> >playing back multi-channel data.  When playing back stereo 
> >data it should be possible to configure the hardware and do 
> >the simulation in the same way as when multi-channel support 
> >is not compiled in and avoid the additional costs which that incurs.
> >
> >As well as saving memory I'd expect configuring this at 
> >runtime to also save some power when playing back two or four 
> >channel data.
> >
> 
> Yes, it's an ideal way,but it's not safe to allocate continuous memory
> dynamicly,
> Since embedded system has limited uncached DMA memory.

But, CONFIG_SND_MULTICHAN_SUPPORT would change any buffer allocation
behavior?  I don't find it...

Anyway, I agree with Mark.  The setup can be ideally dynamically
changed.


thanks,

Takashi