[alsa-devel] About the platform_name field in snd_soc_dai_link

Liam Girdwood lrg at slimlogic.co.uk
Tue Aug 10 16:16:09 CEST 2010

On Tue, 2010-08-10 at 14:47 +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.
> > 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.
> _______________________________________________

With multi-component it's possible to register both FIQ and DMA platform
together. i.e. ssi0 could use DMA and ssi1 FIQ. 

So for OMAP4 I have two platforms. One is the SDMA driver and the other
a DSP. So I could have the following DAI link :-

static struct snd_soc_dai_link sdp4430_dai[] = {
	.name = "TWL6040-SDMA",
	.stream_name = "TWL6040",
	.cpu_dai_name ="omap-mcpdm-dai",
	.codec_dai_name = "twl6040-hifi",
	.platform_name = "omap-pcm-audio",  <<<< SDMA audio device
	.codec_name = "twl6040-codec",
	.init = sdp4430_twl6040_init,
	.ops = &sdp4430_ops,
}, {
	.name = "TWL6040-DSP",
	.stream_name = "TWL6040",
	.cpu_dai_name ="omap-mcpdm-dai",
	.codec_dai_name = "twl6040-hifi",
	.platform_name = "omap-dsp-audio",   <<< DSP audio device.
	.codec_name = "twl6040-codec",
	.init = sdp4430_twl6040_init,
	.ops = &sdp4430_ops,

The snd_soc_dai_set_dma_data() can be used to pass DMA type data between
the SSI ports and FIQ/SDMA components.


Freelance Developer, SlimLogic Ltd
ASoC and Voltage Regulator Maintainer.

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