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

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Date:   Wed, 27 Sep 2017 14:46:11 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "Peter De Schrijver" <pdeschrijver@...dia.com>,
        Prashant Gaikwad <pgaikwad@...dia.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Vinod Koul <vinod.koul@...el.com>
CC:     <linux-tegra@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <dmaengine@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 3/5] dt-bindings: Add DT bindings for NVIDIA Tegra AHB
 DMA controller


On 27/09/17 14:44, Jon Hunter wrote:
> 
> On 27/09/17 13:12, Dmitry Osipenko wrote:
>> 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@...il.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.
> 
> TRM shows the following in the APBDMA_TRIG_REG_0 ...
> 
> "XRQ_A: XRQ.A (GPIOA) (Hardware initiated DMA request)"

Furthermore there are timer and hw-semaphore triggers as well.

Jon

-- 
nvpublic