RE: [EXT] Re: [PATCH v2 1/3] dt-bindings: usb: cdns-imx8qm: add imx8qm cdns3 glue bindings

[Frank Li]

> -----Original Message-----
> From: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> Sent: Monday, March 20, 2023 11:27 AM
> To: Frank Li <frank.li@xxxxxxx>; shawnguo@xxxxxxxxxx
> Cc: devicetree@xxxxxxxxxxxxxxx; festevam@xxxxxxxxx; imx@xxxxxxxxxxxxxxx;
> kernel@xxxxxxxxxxxxxx; krzysztof.kozlowski+dt@xxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>; linux-
> kernel@xxxxxxxxxxxxxxx; robh+dt@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx
> Subject: Re: [EXT] Re: [PATCH v2 1/3] dt-bindings: usb: cdns-imx8qm: add
> imx8qm cdns3 glue bindings
> 
> Caution: EXT Email
> 
> On 20/03/2023 17:22, Frank Li wrote:
> >>>>>>> +  assigned-clocks:
> >>>>>>> +    items:
> >>>>>>> +      - description: Phandle and clock specifier of
> >> IMX_SC_PM_CLK_PER.
> >>>>>>> +      - description: Phandle and clock specifoer of
> >>>> IMX_SC_PM_CLK_MISC.
> >>>>>>> +      - description: Phandle and clock specifoer of
> >>>>>> IMX_SC_PM_CLK_MST_BUS.
> >>>>>>> +
> >>>>>>> +  assigned-clock-rates:
> >>>>>>> +    items:
> >>>>>>> +      - description: Must be 125 Mhz.
> >>>>>>> +      - description: Must be 12 Mhz.
> >>>>>>> +      - description: Must be 250 Mhz.
> >>>>>>
> >>>>>> I would argue that both properties above are not needed. If your
> >>>>>> hardware requires fixed frequencies, clock provider can fix them,
> can't
> >> it?
> >>>>>
> >>>>> Clock provider don't know fixed value and turn on only used by client.
> >>>>
> >>>> So maybe fix the clock provider? Or this device driver? Requiring by
> >>>> binding specific frequencies for every board is a bit redundant.
> >>>
> >>> It is not for every boards, it is common for a chip family.  Only a place to
> set
> >> for
> >>> QM and QXP.
> >>>
> >>> The similar case is network driver, which require a specific frequency at
> >> clock assign.
> >>> Generally frequency is fixed,  clock source name may change at
> difference
> >> chips.
> >>
> >> If frequency is always fixed, I don't understand why this is in DT
> >> bindings. I would even say it should not be in DTS. We don't put into
> >> DTS properties which are always the same, because otherwise they would
> >> grow crazy big.
> >
> > Although frequency is fixed, clock name may change for difference
> platform.
> >
> >                 assigned-clocks = <&clk IMX_SC_R_USB_2 IMX_SC_PM_CLK_PER>,
> >                                            <&clk IMX_SC_R_USB_2 IMX_SC_PM_CLK_MISC>,
> >                                            <&clk IMX_SC_R_USB_2
> IMX_SC_PM_CLK_MST_BUS>;
> >                assigned-clock-rates = <125000000>, <12000000>, <250000000>;
> >
> > some platform use IMX_SC_R_USB_2, other platform may use
> IMX_SC_R_USB_3.
> 
> This I understand, you wrote it above, so nothing new and my concerns
> are still there.

I think Fixed value is not good reason. All reg base address, irq number are all for fixed number. The same
Logic can be applied to irq-provider driver. But why still be descript in dts? It is hardware property.    

https://elixir.bootlin.com/linux/v4.8/source/Documentation/devicetree/bindings/clock/clock-bindings.txt
have not said that can't set to fixed clock frequency. 

This is quick common case for network, USB, SATA, PCIE,  which protocol defined
Frequency.  

https://elixir.bootlin.com/linux/v6.3-rc3/source/Documentation/devicetree/bindings/ata/qcom-sata.txt
https://elixir.bootlin.com/linux/v6.3-rc3/source/Documentation/devicetree/bindings/usb/qcom,dwc3.yaml

Such frequency information is necessary.  We can put to dts or clock drivers.  The clock driver
Become bigger, or dts become bigger.  I think the key point is if property to descript hardware information.  

> 
> Best regards,
> Krzysztof