[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 17:48:56 +0800,
Cai, Cliff wrote:
> 
>  
> 
> >-----Original Message-----
> >From: Takashi Iwai [mailto:tiwai at suse.de] 
> >Sent: Tuesday, October 21, 2008 5:39 PM
> >To: Cai, Cliff
> >Cc: Mark Brown; Bryan Wu; alsa-devel at alsa-project.org
> >Subject: Re: [alsa-devel] [PATCH 2/3] ASoC: Blackfin: add 
> >multi-channel supporting in Blackfin ASoC driver and AD1980 
> >codec driver
> >
> >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...
> 
> It will change the ac97 frame size defined in bf5xx-ac97.h,the frame
> size the basic unit of the DMA buffer 

Ah, I see.  Then I find this patch OK, at least, changes for blackfin
part.
Basically MULTICHAN_SUPPORT will require more resources, but it still
provides the same functionality as without it.

BTW, are your changes to ad1980.c applicable unconditionally?
For example,
> --- a/sound/soc/codecs/ad1980.c
> +++ b/sound/soc/codecs/ad1980.c
> @@ -145,7 +145,7 @@ struct snd_soc_dai ad1980_dai = {
>  	.playback = {
>  		.stream_name = "Playback",
>  		.channels_min = 2,
> -		.channels_max = 2,
> +		.channels_max = 6,

This won't work if the machine side doesn't support the
multi-channel.  Right now, blackfin is the only one, but the codec
driver should be generic.

Also, the below is dangerous:

> @@ -256,6 +256,9 @@ static int ad1980_soc_probe(struct platform_device *pdev)
> +	ac97_write(codec, AC97_EXTENDED_STATUS, 0x0000);/*power on LFE CENTER and Surround DACs*/

This will disable all other features, too.


thanks,

Takashi