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

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Message-ID: <6fddfd9a-8a8c-4dae-9f74-e8019b7ed404@pengutronix.de>
Date: Mon, 6 Jan 2025 20:55:08 +0100
From: Ahmad Fatoum <a.fatoum@...gutronix.de>
To: Frank Li <Frank.li@....com>, Conor Dooley <conor+dt@...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, 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 20:42, Frank Li wrote:
> On Mon, Jan 06, 2025 at 08:25:38PM +0100, Ahmad Fatoum wrote:
>> On 06.01.25 17:41, Frank Li wrote:
>>> On Mon, Jan 06, 2025 at 03:21:42PM +0100, Ahmad Fatoum wrote:
>>>> 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"]

I don't see myself setting this via overlay, but if you say it's useful, we can
adjust the binding.

I am not sure what's the preference is though, should we have

  fsl,operating-mode = "normal" / "overdrive"

or 

  fsl,operating-mode = <IMX_OPMODE_NORMAL> / <IMX_OPMODE_OVERDRIVE>


Any idea? Conor?

Cheers,
Ahmad

> 
> 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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> 


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