On 02.10.2017 20:05, Stephen Warren wrote: > On 09/29/2017 09:11 PM, Dmitry Osipenko wrote: >> 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. > > The request selector cell isn't optional, so is always present. If we later add > an optional trig_sel cell, we'll either have: > > #dma-cells=<1>: req_sel > > or: > > #dma-cells=<2>: req_sel, trig_sel Why request sel. couldn't be optional? Could you please elaborate a bit more? I think possible options are: #dma-cells=<1>: req_sel #dma-cells=<1>: trig_sel #dma-cells=<2>: req_sel, trig_sel The only difference between request and trigger is that trigger issues the whole transfer, while request only a single burst. Isn't it possible to have a case in HW for the "trigger-only" option? If not or it's a rareness, then I agree that REQ_SEL must be mandatory. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
