linux-kernel - Re: [PATCH v2 1/6] dt-bindings: clock: imx8m: document nominal/overdrive properties

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Message-ID: <Z3wyG61QEzgCJFh+@lizhi-Precision-Tower-5810>
Date: Mon, 6 Jan 2025 14:42:19 -0500
From: Frank Li <Frank.li@....com>
To: Ahmad Fatoum <a.fatoum@...gutronix.de>
Cc: Abel Vesa <abelvesa@...nel.org>, Peng Fan <peng.fan@....com>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Abel Vesa <abel.vesa@...aro.org>, Marek Vasut <marex@...x.de>,
	linux-clk@...r.kernel.org, imx@...ts.linux.dev,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Conor Dooley <conor.dooley@...rochip.com>
Subject: Re: [PATCH v2 1/6] dt-bindings: clock: imx8m: document
 nominal/overdrive properties

On Mon, Jan 06, 2025 at 08:25:38PM +0100, Ahmad Fatoum wrote:
> Hello Frank,
>
> On 06.01.25 17:41, Frank Li wrote:
> > On Mon, Jan 06, 2025 at 03:21:42PM +0100, Ahmad Fatoum wrote:
>
> [snip]
>
> >> Allowing for absence of both properties is
> >> needed, because there is no default suitable for all boards:
> >>
> >> For i.MX8M Mini and Nano, the kernel SoC DTSIs has assigned-clock-rates
> >> that are all achievable in nominal mode. For i.MX8MP, there are some
> >> rates only validated for overdrive mode.
> >>
> >> But even for the i.MX8M Mini/Nano boards, we don't know what rates they
> >> may configure at runtime, so it has not been possible so far to infer from
> >> just the device tree what the mode is.
>
> [snip]
>
> >> +  fsl,nominal-mode:
> >> +    description: Set if SoC is operated in nominal mode
> >> +    $ref: /schemas/types.yaml#/definitions/flag
> >> +
> >> +  fsl,overdrive-mode:
> >> +    description: Set if SoC is operated in overdrive mode
> >> +    $ref: /schemas/types.yaml#/definitions/flag
> >> +
> >
> > why need two flags? suppose "not set fsl,overdrive-mode" is equal to
> > fsl,nominal-mode
>
> Conor had the same question on v1[1] and I have addressed this in the commit
> message of v2, see above.
>
> In short, there is unfortunately no universally applicable default.
>
> [1]: https://lore.kernel.org/all/4e2250b3-5170-4e88-aa0a-dd796b81e78b@pengutronix.de/
>

But there are problem if use dts overlay because dts overlay can't support
delete property.

If one dts file use "fsl,overdrive-mode", dts overlay file can't delete
this property. "mutually exclusive optional properties" was not preferred.

mode = ["normal" | "overdrive"]

Frank

> Thanks,
> Ahmad
>
>
> >
> > Frank
> >
> >>  required:
> >>    - compatible
> >>    - reg
> >> @@ -95,6 +103,12 @@ allOf:
> >>              - const: clk_ext2
> >>              - const: clk_ext3
> >>              - const: clk_ext4
> >> +  - if:
> >> +      required:
> >> +        - fsl,overdrive-mode
> >> +    then:
> >> +      properties:
> >> +        fsl,nominal-mode: false
> >>
> >>  additionalProperties: false
> >>
> >>
> >> --
> >> 2.39.5
> >>
> >
>
>
> --
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