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

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Message-ID: <b8801c83-f2dc-f144-de58-03e5c24436fd@linaro.org>
Date:   Mon, 20 Mar 2023 16:23:01 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Frank Li <frank.li@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>
Cc:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "festevam@...il.com" <festevam@...il.com>,
        "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        dl-linux-imx <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>
Subject: Re: [EXT] Re: [PATCH v2 1/3] dt-bindings: usb: cdns-imx8qm: add
 imx8qm cdns3 glue bindings

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