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

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Message-ID: <8a8f315b-9e6b-4c18-985e-5df4ecbe34da@pengutronix.de>
Date: Thu, 26 Dec 2024 17:54:15 +0100
From: Ahmad Fatoum <a.fatoum@...gutronix.de>
To: Conor Dooley <conor@...nel.org>
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

Hi Conor,

On 25.12.24 15:20, Conor Dooley wrote:
> On Thu, Dec 19, 2024 at 09:14:10PM +0100, Ahmad Fatoum wrote:
>> On 19.12.24 20:49, Conor Dooley wrote:
>>> On Thu, Dec 19, 2024 at 08:27:32AM +0100, Ahmad Fatoum wrote:
>> Theoretically, we could infer mode at runtime from VDD_SOC voltage,
>> but we need to set up clocks to read out the PMIC and I want to
>> apply the constraints as early as possible as I don't want the SoC
>> to run outside of spec even for a short while.
> 
> Apologies for the delay responding to you, doing it today cos I feel
> guilty!

I am fully aware that I needn't expect prompt review feedback so late in
December. Thanks a lot for taking the time still.

> I think what you've explained here is fine, but could you add a
> bit more of that info to the commit message, explaining why one cannot
> be default? With that,
> Acked-by: Conor Dooley <conor.dooley@...rochip.com>

Thanks. I will await further review feedback and adjust this commit's
message for v2 as requested.

Wishing you nice holidays,
Ahmad

> 
> Cheers,
> Conor.
> 
>>
>> Thanks,
>> Ahmad
>>
>>>
>>>>
>>>> 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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>> 31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
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-- 
Pengutronix e.K.                           |                             |
Steuerwalder Str. 21                       | http://www.pengutronix.de/  |
31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    |
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