linux-kernel - Re: [PATCH 1/2] dt-bindings: clock: imx8m: introduce fsl,protected-clocks property

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Date:   Tue, 16 Aug 2022 10:14:07 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Peng Fan <peng.fan@....com>
Cc:     "Peng Fan (OSS)" <peng.fan@....nxp.com>,
        "abelvesa@...nel.org" <abelvesa@...nel.org>,
        "abel.vesa@...aro.org" <abel.vesa@...aro.org>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        dl-linux-imx <linux-imx@....com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/2] dt-bindings: clock: imx8m: introduce
 fsl,protected-clocks property

On Tue, Aug 16, 2022 at 07:13:27AM +0000, Peng Fan wrote:
> Hi Sascha,
> 
> > Subject: Re: [PATCH 1/2] dt-bindings: clock: imx8m: introduce fsl,protected-
> > clocks property
> > 
> > Hi Peng,
> > 
> > On Mon, Aug 15, 2022 at 11:36:31AM +0800, Peng Fan (OSS) wrote:
> > > From: Peng Fan <peng.fan@....com>
> > >
> > > i.MX8M Linux run on top of Jailhouse hypervisor, the root cell Linux
> > > should not disable clocks used by inmate. This would also benifit AMP
> > > to avoid Linux disable clocks used by Cortex-M4/M7.
> > >
> > > So introduce fsl,protected-clocks for above case.
> > >
> > > Signed-off-by: Peng Fan <peng.fan@....com>
> > > ---
> > >  Documentation/devicetree/bindings/clock/imx8m-clock.yaml | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
> > > b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
> > > index 458c7645ee68..0ec490ff9a09 100644
> > > --- a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
> > > +++ b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
> > > @@ -39,6 +39,10 @@ properties:
> > >        ID in its "clocks" phandle cell. See include/dt-bindings/clock/imx8m-
> > clock.h
> > >        for the full list of i.MX8M clock IDs.
> > >
> > > +  fsl,protected-clocks:
> > > +    description: List of the Protected clock.
> > > +    $ref: /schemas/types.yaml#/definitions/uint32-array
> > 
> > There already is a generic protected-clocks property described in
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithu
> > b.com%2Fdevicetree-org%2Fdt-
> > schema%2Fblob%2F0d1b78cd0c3d9a3d523ced17d7da64b03f6c18ea%2Fdtsc
> > hema%2Fschemas%2Fclock%2Fclock.yaml%23L131&amp;data=05%7C01%7
> > Cpeng.fan%40nxp.com%7C5dbc72639c9147765af208da7ec63315%7C686ea
> > 1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637961686968811809%7CUn
> > known%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI
> > 6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=D%2BfJA5h
> > wblaX8VH%2BdQoN0pEFmCipfZHHf0ZVo07B4kg%3D&amp;reserved=0
> > We probably shouldn't add a property with the same name but different
> > meaning.
> > 
> 
> Thanks for sharing the info. I should check the common bindings before
> cook this patchset.
> 
> > I am not sure if we want to go the route of a fsl specific property, it looks
> > like other SoCs could have similar problems and it might be worth solving
> > this problem with a broader view.
> > 
> 
> I see qcom just drop the clock entries before registering the clocks. But to
> i.MX8M, it is not feasible to drop those clocks, unless check the
> protected-clocks property before registering every clock. This is odd.
> 
> So here I just wanna let i.MX8M clk driver prepare enable the clocks listed
> in protected-clocks property to avoid linux disable those clocks.
> > Anyway, please add a description to the binding what this property actually
> > does.
> I will switch to use the common bindings.

There were cases when a property first started with a "soc," prefix and
later when people realized that it could be useful for other
drivers/SoCs as well, the prefix was removed. With that in mind I
would expect that a "fsl,protected-clocks" property behaves the same
as a "protected-clocks" property without the prefix.

If it doesn't please pick a different name. I didn't want to suggest
to just drop the "fsl," prefix and to use the generic property name
when the properties have a different meaning.

Sascha

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