Re: [PATCH v1 3/5] dt-bindings: Add DT bindings for NVIDIA Tegra AHB DMA controller

[Dmitry Osipenko <digetx@gmail.com>]

On 27.09.2017 11:34, Jon Hunter wrote:
> 
> On 27/09/17 02:57, Dmitry Osipenko wrote:
>> On 26.09.2017 17:50, Jon Hunter wrote:
>>>
>>> On 26/09/17 00:22, Dmitry Osipenko wrote:
>>>> Document DT bindings for NVIDIA Tegra AHB DMA controller that presents
>>>> on Tegra20/30 SoC's.
>>>>
>>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
>>>> ---
>>>>  .../bindings/dma/nvidia,tegra20-ahbdma.txt         | 23 ++++++++++++++++++++++
>>>>  1 file changed, 23 insertions(+)
>>>>  create mode 100644 Documentation/devicetree/bindings/dma/nvidia,tegra20-ahbdma.txt
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/dma/nvidia,tegra20-ahbdma.txt b/Documentation/devicetree/bindings/dma/nvidia,tegra20-ahbdma.txt
>>>> new file mode 100644
>>>> index 000000000000..2af9aa76ae11
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/dma/nvidia,tegra20-ahbdma.txt
>>>> @@ -0,0 +1,23 @@
>>>> +* NVIDIA Tegra AHB DMA controller
>>>> +
>>>> +Required properties:
>>>> +- compatible:	Must be "nvidia,tegra20-ahbdma"
>>>> +- reg:		Should contain registers base address and length.
>>>> +- interrupts:	Should contain one entry, DMA controller interrupt.
>>>> +- clocks:	Should contain one entry, DMA controller clock.
>>>> +- resets :	Should contain one entry, DMA controller reset.
>>>> +- #dma-cells:	Should be <1>. The cell represents DMA request select value
>>>> +		for the peripheral. For more details consult the Tegra TRM's
>>>> +		documentation, in particular AHB DMA channel control register
>>>> +		REQ_SEL field.
>>>
>>> What about the TRIG_SEL field? Do we need to handle this here as well?
>>>
>>
>> Actually, DMA transfer trigger isn't related a hardware description. It's up to
>> software to decide what trigger to select. So it shouldn't be in the binding.
> 
> I think it could be, if say a board wanted a GPIO to trigger a transfer.
> 

GPIO isn't a very good example, there is no "GPIO" trigger. To me all triggers
are software-defined, so that software could create transfer chains.

>> And I think the same applies to requester... any objections?
> 
> Well, the REQ_SEL should definitely be in the binding.
> 

Okay.

> Laxman, Stephen, what are your thoughts on the TRIG_SEL field? Looks
> like we never bothered with it for the APB DMA and so maybe no ones uses
> this.
> 

-- 
Dmitry