[alsa-devel] About the platform_name field in snd_soc_dai_link

[Sascha Hauer]

On Tue, Aug 10, 2010 at 02:47:55PM +0100, Mark Brown wrote:
> On Tue, Aug 10, 2010 at 03:38:18PM +0200, Sascha Hauer wrote:
> 
> > I'm wondering what exactly a snd_soc_platform is. Apparently the
> > snd_pcm_ops/pcm_new/pcm_free are specific to a platform. For my
> > understanding these operations are more specific to a cpu_dai. Looking
> > at the tree it seems that each cpu_dai has exactly one possible
> > platform, which seems logical to me because the cpu_dai knows how to
> > transfer the data.
> 
> They're for the DMA bit of the CPU.  While most platforms have a single
> DMA controller (though some have more than one) it's moderately common
> to have more than one DAI (eg, dedicated I2S and DSP mode controllers
> rather than a programmable serial port, or an AC'97 controller) so it's
> useful to share the DMA code.

I didn't want to question that it's useful to share the code. It's just
that in current i.MX implementation it would be simple to instantiate
snd_pcm_ops (of fiq or dma type) in the platform_driver probe function
passing all needed data like dma request line, fifo address and the like.
Passing this data through the soc-core seems not very convenient.

> 
> > My problem on i.MX is that I currently have two possible cpu dais
> > (imx-ssi.[01]) and each can be configured to use dma or fiq depending
> > on the dma capabilities. So the cpu_dai knows which pcm_ops we have
> > to use, but currently it's the soc glue code which has to decide in
> > platform_name. Am I understanding something wrong here?
> 
> This is mostly a holdover from the existing (current mainline) ASoC
> structuring at the minute, that also has the DMA configured per machine.
> This may change depending on future hardware requirements, though.

I would welcome such change.

/Me is looking further to make the i.MX part working on multi-component.

Sascha

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