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

[Krzysztof Kozlowski]

On 20/03/2023 15:49, Frank Li wrote:
>>>>> +  clock-names:
>>>>> +    items:
>>>>> +      - const: usb3_lpm_clk
>>>>> +      - const: usb3_bus_clk
>>>>> +      - const: usb3_aclk
>>>>> +      - const: usb3_ipg_clk
>>>>> +      - const: usb3_core_pclk
>>>>> +
>>>>> +  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.

Best regards,
Krzysztof