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

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Message-ID: <cf203807-77ab-463c-b0b0-4a1cec891fe6@acm.org>
Date: Thu, 28 Aug 2025 10:22:28 -0700
From: Bart Van Assche <bvanassche@....org>
To: Ram Kumar Dwivedi <quic_rdwivedi@...cinc.com>, 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 8/28/25 9:45 AM, 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-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.

Hi Ram,

Thanks for having looked this up.

Since it is much more common to refer to these rates as "Rate A" and
"Rate B" rather than using numbers for these rates, please change the
enumeration labels into something like "Rate_A" and "Rate_B".

Thanks,

Bart.