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

[Cai, Cliff]

>-----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.