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

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Message-ID: <8d705694-498a-4592-b93a-7df6a1dd5211@quicinc.com>
Date: Thu, 28 Aug 2025 22:15:10 +0530
From: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>
To: 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 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).

While issuing the DME command from the UFS driver to set the rate,
the values 1 and 2 are passed as arguments for Rate A and Rate B
respectively. Additionally, the hs_rate variable is of type u32.

Thanks,
Ram

> 
> Thanks,
> 
> Bart.