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

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Message-ID: <20241219-lash-lather-31443ced0e0c@spud>
Date: Thu, 19 Dec 2024 19:49:46 +0000
From: Conor Dooley <conor@...nel.org>
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
Subject: Re: [PATCH 1/6] dt-bindings: clock: imx8m: document
 nominal/overdrive properties

On Thu, Dec 19, 2024 at 08:27:32AM +0100, Ahmad Fatoum wrote:
> The imx8m-clock.yaml binding covers the clock controller inside all
> of the i.MX8M Q/M/N/P SoCs. All of them have in common that they
> support two operating modes: nominal and overdrive mode.

This implies that only the two modes you mention are possible, but you
leave the option open to a dts author to use either. How come?

Makes it seem like we only need one of these, for whatever the
non-default option is?

> 
> While the overdrive mode allows for higher frequencies for many IPs,
> the nominal mode needs a lower SoC voltage, thereby reducing
> heat generation and power usage.
> 
> In any case, software should respect the maximum clock rate limits
> described in the datasheet for each of the two operating modes.
> 
> To allow device tree consumers to enforce these limits, document two new
> optional properties that can be used to sanity check the clock tree.
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
> ---
>  Documentation/devicetree/bindings/clock/imx8m-clock.yaml | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
> index c643d4a81478..a6ae5257ef53 100644
> --- a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
> +++ b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
> @@ -43,6 +43,14 @@ 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,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
> +
>  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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