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

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Message-ID: <a3796e76-d597-4c0d-ae7c-d042cce564a5@kernel.org>
Date: Wed, 18 Jun 2025 11:08:25 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Sarthak Garg <quic_sartgarg@...cinc.com>,
 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 18/06/2025 10:38, Sarthak Garg wrote:
> 
> 
> 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.

The are no arguments provided in favor, so my review from v1 stays. You
get the same comments.

Best regards,
Krzysztof