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: <AM6PR04MB4838F5C9EF13A588E799D5C488809@AM6PR04MB4838.eurprd04.prod.outlook.com>
Date:   Mon, 20 Mar 2023 16:22:47 +0000
From:   Frank Li <frank.li@....com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "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

> >>>>> +  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.


> 
> Best regards,
> Krzysztof