linux-kernel - Re: [PATCH V5 2/4] dt-bindings: mmc: controller: Add max-sd-hs-frequency property

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Message-ID: <295e36e0-0fba-4ccc-bcbe-e7bb5ef95be2@quicinc.com>
Date: Thu, 4 Sep 2025 13:37:35 +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_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 V5 2/4] dt-bindings: mmc: controller: Add
 max-sd-hs-frequency property



On 9/3/2025 1:52 PM, Krzysztof Kozlowski wrote:
> On 03/09/2025 10:04, Sarthak Garg wrote:
>> Some platforms may require limiting the maximum frequency used in SD
>> High-Speed (HS) mode due to board-level hardware constraints. For
>> example, certain boards may include level shifters or other components
>> that cannot reliably operate at the default 50 MHz HS frequency.
>>
>> 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.
>>
>> Signed-off-by: Sarthak Garg <quic_sartgarg@...cinc.com>
>> ---
>>   .../devicetree/bindings/mmc/mmc-controller-common.yaml    | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
>> index 9a7235439759..d6b785cb2bd9 100644
>> --- a/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
>> +++ b/Documentation/devicetree/bindings/mmc/mmc-controller-common.yaml
>> @@ -93,6 +93,14 @@ properties:
>>       minimum: 400000
>>       maximum: 384000000
>>   
>> +  max-sd-hs-hz:
>> +    description: |
>> +      Maximum frequency (in Hz) to be used for SD cards operating in
>> +      High-Speed (HS) mode. This is useful for board-specific limitations,
>> +      such as level shifters or others where the card cannot reliably
>> +      operate at the default 50 MHz HS frequency.
>> +    default: 50000000
> 
> no minimum/maximum? If 50 MHz is default, isn't it also an actual max?
> 
> Best regards,
> Krzysztof

I realized I had misinterpreted your earlier comment, which led to the
removal of min/max. I’ll reintroduce them with the following values:

+    minimum: 400000
+    maximum: 50000000
+    default: 50000000

Regarding your comment on V4 — "Don't repeat constraints in free form
text" — just to clarify: are you suggesting that I remove the sentence:

"This is useful for board-specific limitations, such as level shifters
or others where the card cannot reliably operate at the default 50 MHz
HS frequency."

If so, I’ll go ahead and remove it from the bindings.

Best regards,
Sarthak