Re: [PATCH v2 1/8] dt-bindings: PCI: Add binding for qps615

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Mon, Aug 05, 2024 at 07:18:04PM +0200, Krzysztof Kozlowski wrote:
> On 05/08/2024 19:07, Bjorn Andersson wrote:
> > On Mon, Aug 05, 2024 at 09:41:26AM +0530, Krishna Chaitanya Chundru wrote:
> >> On 8/4/2024 2:23 PM, Krzysztof Kozlowski wrote:
> >>> On 03/08/2024 05:22, Krishna chaitanya chundru wrote:
> >>>> diff --git a/Documentation/devicetree/bindings/pci/qcom,qps615.yaml b/Documentation/devicetree/bindings/pci/qcom,qps615.yaml
> > [..]
> >>>> +  qps615,axi-clk-freq-hz:
> >>>> +    description:
> >>>> +      AXI clock which internal bus of the switch.
> >>>
> >>> No need, use CCF.
> >>>
> >> ack
> > 
> > This is a clock that's internal to the QPS615, so there's no clock
> > controller involved and hence I don't think CCF is applicable.
> 
> AXI does not sound that internal.

Well, AXI is applicable to whatever entity that implements it. We mostly seen it
in ARM SoCs (host), but in this case the PCIe switch also has a microcontroller
/processor of some sort, so AXI is indeed relevant for it. The naming actually
comes from the switch's i2c register name that is being configured in the driver
based on this property value.

> DT rarely needs to specify internal
> clock rates. What if you want to define rates for 20 clocks? Even
> clock-frequency is deprecated, so why this would be allowed?
> bus-frequency is allowed for buses, but that's not the case here, I guess?
> 

This clock frequency is for the switch's internal AXI bus that runs at default
200MHz. And this property is used to specify a frequency that is configured over
the i2c interface so that the switch's AXI bus can operate in a low frequency
there by reducing the power consumption of the switch.

It is not strictly needed for the switch operation, but for power optimization.
So this property can also be dropped for the initial submission and added later
if you prefer.

- Mani

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