linux-kernel - Re: [PATCH V3 1/4] ufs: dt-bindings: Document gear and rate limit properties

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Message-ID: <c73b16e5-bc48-493d-a1a7-06b779a7a7ab@kernel.org>
Date: Thu, 28 Aug 2025 19:41:50 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>,
 Bart Van Assche <bvanassche@....org>, alim.akhtar@...sung.com,
 avri.altman@....com, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, mani@...nel.org, James.Bottomley@...senPartnership.com,
 martin.petersen@...cle.com
Cc: linux-scsi@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH V3 1/4] ufs: dt-bindings: Document gear and rate limit
 properties

On 28/08/2025 18:45, Ram Kumar Dwivedi wrote:
> 
> 
> On 26-Aug-25 9:05 PM, Bart Van Assche wrote:
>> On 8/26/25 8:08 AM, Ram Kumar Dwivedi wrote:
>>> +  limit-hs-gear:
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>> +    minimum: 1
>>> +    maximum: 5
>>> +    default: 5
>>> +    description:
>>> +      Restricts the maximum HS gear used in both TX and RX directions,
>>> +      typically for hardware or power constraints in automotive use cases.
>>
>> The UFSHCI 5.0 spec will add gear 6 soon. So why to restrict the maximum
>> gear to 5?
>>
>>> +  limit-rate:
>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>> +    enum: [1, 2]
>>> +    default: 2
>>> +    description:
>>> +      Restricts the UFS controller to Rate A (1) or Rate B (2) for both
>>> +      TX and RX directions, often required in automotive environments due
>>> +      to hardware limitations.
>>
>> As far as I know no numeric values are associated with these rates in
>> the UFSHCI 4.1 standard nor in any of the previous versions of this
>> standard. Does the .yaml syntax support something like "enum: [A, B]"?
> Hi Bart,
> 
> As per the MIPI UniPro spec:
> 
> In Section 5.7.12.3.2, the hs_series is defined as:
> hs_series = Flags[3] + 1;
> 
> In Section 5.7.7.1, Flags[3] is described as:
> Set to ‘0’ for Series A and ‘1’ for Series B (PA_HSSeries).

That's register value. Why are you using values as argument of actual
meaning of rates?


Best regards,
Krzysztof