On 29.09.2017 22:30, Stephen Warren wrote: > On 09/27/2017 02:34 AM, 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@xxxxxxxxx> >>>>> --- >>>>> .../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. >> >>> And I think the same applies to requester... any objections? >> >> Well, the REQ_SEL should definitely be in the binding. >> >> 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. > > I don't think TRIG_SEL should be in the binding, at least at present. While > TRIG_SEL certainly is something used to configure the transfer, I believe the > semantics of the current DMA binding only cover DMA transfers that are initiated > when SW desires, rather than being a combination of after SW programs the > transfer plus some other HW event. So, we always use a default/hard-coded > TRIG_SEL value. As such, there's no need for a TRIG_SEL value in DT. There's > certainly no known use-case that requires a non-default TRIG_SEL value at > present. We could add an extra #dma-cells value later if we find a use for it, > and the semantics of that use-case make sense to add it to the DMA specifier, > rather than some other separate higher-level property/driver/... Thank you for the comment. If we'd want to extend the binding further with the trigger, how to differentiate trigger from the requester in a case of a single #data-cell? Of course realistically a chance that the further extension would be needed is very-very low, so we may defer the efforts to solve that question and for now make driver aware of the potential #dma-cells extension. -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
