linux-kernel - Re: [PATCH v3 1/6] dt-bindings: clock: imx8m: document nominal/overdrive properties

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Message-ID: <45bbdacc-6683-43df-b7ff-d3bd09842f65@pengutronix.de>
Date: Mon, 13 Jan 2025 17:09:19 +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
Subject: Re: [PATCH v3 1/6] dt-bindings: clock: imx8m: document
 nominal/overdrive properties

On 13.01.25 16:58, Frank Li wrote:
> On Mon, Jan 13, 2025 at 02:42:51PM +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.
>>
>> 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.
>>
>> As increasing clock rates beyond the maximum permitted by the supplied
>> SoC voltage can lead to difficult to debug issues, device tree consumers
>> would benefit from knowing what mode is active to enforce the clock rate
>> limits that come with it.
>>
>> To facilitate this, extend the clock controller bindings with an
>> optional fsl,operating-mode property. This intentionally allows the
>> absence of the property, 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.
>>
>> Signed-off-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
>> ---
>>  Documentation/devicetree/bindings/clock/imx8m-clock.yaml | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
>> index c643d4a814786a1fc7e559140fe58911990f71bb..b03672255cae9462013a8a4e7a2adaff440f1420 100644
>> --- a/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
>> +++ b/Documentation/devicetree/bindings/clock/imx8m-clock.yaml
>> @@ -43,6 +43,16 @@ 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,operating-mode:
>> +    $ref: /schemas/types.yaml#/definitions/string
>> +    description:
>> +      The operating mode of the SoC. This affects the maximum clock rates that
>> +      can safely be configured by the clock controller.
>> +    oneOf:
>> +      - enum:
>> +          - nominal
>> +          - overdrive
> 
> I remember
> 
> fsl,operating-mode:
>   enum: [nominal, overdrive]
> 
> should work without oneOf

Yes, you're right. This is a left-over from the example I copy-pasted from.
Thanks, will fix for v4. Feel free to leave some Reviewed-by on the
other patches though in the mean-time. :-)

Cheers,
Ahmad

> 
> Frank
> 
> 
>> +
>>  required:
>>    - compatible
>>    - reg
>> @@ -109,6 +119,7 @@ examples:
>>                   <&clk_ext3>, <&clk_ext4>;
>>          clock-names = "osc_32k", "osc_24m", "clk_ext1", "clk_ext2",
>>                        "clk_ext3", "clk_ext4";
>> +        fsl,operating-mode = "nominal";
>>      };
>>
>>    - |
>>
>> --
>> 2.39.5
>>
> 


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