linux-kernel - Re: [PATCH V3 2/4] dt-bindings: mmc: controller: Add max-sd-hs-frequency property

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Message-ID: <d1ffbcf5-967a-4c1e-9f2c-becc5fb6c6ed@quicinc.com>
Date: Wed, 18 Jun 2025 14:08:43 +0530
From: Sarthak Garg <quic_sartgarg@...cinc.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Ulf Hansson
	<ulf.hansson@...aro.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski
	<krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Adrian Hunter
	<adrian.hunter@...el.com>
CC: <linux-mmc@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <quic_cang@...cinc.com>, <quic_nguyenb@...cinc.com>,
        <quic_rampraka@...cinc.com>, <quic_pragalla@...cinc.com>,
        <quic_sayalil@...cinc.com>, <quic_nitirawa@...cinc.com>,
        <quic_bhaskarv@...cinc.com>, <kernel@....qualcomm.com>
Subject: Re: [PATCH V3 2/4] dt-bindings: mmc: controller: Add
 max-sd-hs-frequency property



On 6/18/2025 1:13 PM, Krzysztof Kozlowski wrote:
> On 18/06/2025 09:28, Sarthak Garg wrote:
>> Introduce a new optional device tree property `max-sd-hs-frequency` to
>> limit the maximum frequency (in Hz) used for SD cards operating in
>> High-Speed (HS) mode.
>>
>> This property is useful for platforms with vendor-specific hardware
>> constraints, such as the presence of a level shifter that cannot
>> reliably support the default 50 MHz HS frequency. It allows the host
>> driver to cap the HS mode frequency accordingly.
>>
>> Signed-off-by: Sarthak Garg <quic_sartgarg@...cinc.com>
>> ---
>>   .../devicetree/bindings/mmc/mmc-controller-common.yaml | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
>> index 9a7235439759..1976f5f8c401 100644
>> --- a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
>> +++ b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
>> @@ -93,6 +93,16 @@ properties:
>>       minimum: 400000
>>       maximum: 384000000
>>   
>> +  max-sd-hs-frequency:
>> +    $ref: /schemas/types.yaml#/definitions/uint32
>> +    description: |
>> +      Maximum frequency (in Hz) to be used for SD cards operating in
>> +      High-Speed (HS) mode. This is useful for platforms with vendor-specific
>> +      limitations, such as the presence of a level shifter that cannot support
>> +      the default 50 MHz HS frequency or other.
>> +    minimum: 400000
>> +    maximum: 50000000
> 
> This might be fine, but your DTS suggests clearly this is SoC compatible
> deducible, which I already said at v1.
> 
> So now you send v3 which is the same as v1, so you get the same comments.
> 
> Best regards,
> Krzysztof

Introducing this flag no longer becomes SoC compatible because as per 
discussions in V2 patchset with Ulf and Konrad this new property can be 
used by any vendor who wants to limit the HS mode frequency due to any 
reason. Thats why moved to this generic approach again in V3 as compared 
to compatible based approach in V2.