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

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Message-ID: <957ad153-17f3-4cb8-8878-73093a9a2724@pengutronix.de>
Date: Mon, 6 Jan 2025 20:25:38 +0100
From: Ahmad Fatoum <a.fatoum@...gutronix.de>
To: Frank Li <Frank.li@....com>
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

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/

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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