DT DMA channel binding for Tegra I2S

[Stephen Warren]

Rob Herring wrote at Wednesday, November 23, 2011 2:55 PM:
> On 11/23/2011 03:25 PM, Stephen Warren wrote:
> > Rob, Grant,
> >
> > Re: http://www.spinics.net/lists/arm-kernel/msg148899.html
> >
> > Background: Tegra's DMA controller needs to be told which DMA "request
> > select" to use for each transfer. The identifies which peripheral to
> > transfer to/from.
> >
> > The Tegra I2S driver needs to know its own "request select" value to
> > pass to the audio driver DMA path. The board files typically provide
> > this to the driver as an IORESOURCE_DMA. I don't think there's any
> > standard binding that creates such a resource when instantiating a
> > platform device from device tree, and the discussions I found when
> > looking for one didn't seem to reach conclusion that there should be
> > one. So, I proposed the following property in the I2S driver's DT
> > binding for this:
> 
> I think this is a case of every platform being different and
> IORESOURCE_DMA is not too widely used. Even on PPC, there's not a
> standard way.
> 
> > Doc:
> >
> > - dma-channel : The Tegra DMA controller's channel ID for this I2S controller
> >
> > Example:
> >
> > i2s at 70002800 {
> > 	compatible = "nvidia,tegra20-i2s";
> > 	reg = <0x70002800 0x200>;
> > 	interrupts = < 45 >;
> > 	dma-channel = < 2 >;
> > };
> >
> > Does that look reasonable? Or, should I pursue some more standardized
> > solution?
> 
> I had some discussion with Thomas Abraham about this for the pl330 dma:
> 
> http://lists.ozlabs.org/pipermail/devicetree-discuss/2011-September/008269.html
> 
> So I would just add a phandle to the dma controller here.

So you mean just modify the binding as follows:

apbdma: dma at NNNNN { ... };

i2s at 70002800 {
	dma-channel = < &apbdma, 2 >;
};

... and leave the code I quoted as-is?

I /think/ the rest of the patch you linked isn't really relevant to Tegra
at present, since it isn't ported to the DMA engine (yet?).

Thanks.

-- 
nvpublic