DT DMA channel binding for Tegra I2S

[Rob Herring]

On 11/23/2011 05:26 PM, Stephen Warren wrote:
> 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?

Right.

Although, I think you are possibly missing some other properties for
i2s mode like word size and master/slave mode. I think the ideal case
is that a single ASoC platform driver for DT could handle multiple
SoCs.

>
> 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?).
>

Yes, of course..

Rob