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: <fc5c76d1-51cd-5992-9bfa-06f57874fc03@linaro.org>
Date:   Mon, 20 Mar 2023 17:27:22 +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 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.

Best regards,
Krzysztof