Subject: Re: [PATCH v6 1/2] dt-bindings: ufs: Document static TX Equalization settings properties

From: Can Guo <[email-masked]>
Date: Sat, 30 May 2026 21:57:37 +0800

On 5/30/2026 8:45 PM, Can Guo wrote:
>
>
> On 5/30/2026 12:58 AM, Krzysztof Kozlowski wrote:
>> On Fri, May 29, 2026 at 04:33:37AM -0700, Can Guo wrote:
>>> UFS v5.0/UFSHCI v5.0 add HS-G6 support (46.6 Gbps/lane) via UniPro v3.0
>>> and M-PHY v6.0. In these specs, TX Equalization is defined for all High
>>> Speed Gears (not only HS-G6) to compensate channel loss and improve 
>>> signal
>>> integrity at high speed operation.
>>>
>>> For HS-G6, M-PHY uses PAM4 1b1b line coding, Pre-Coding may also be
>>> required depending on channel characteristics.
>>>
>>> Add vendor-neutral DT properties:
>>>
>>> - patternProperties for txeq-preshoot-g[1-6] and txeq-deemphasis-g[1-6]
>>> - fixed property tx-precode-enable-g6
>>>
>>> Each property is a uint32 array of per-lane tuples:
>>> <Host_Lane0 Device_Lane0>, [<Host_Lane1 Device_Lane1>]
>>>
>>> Accept 2 or 4 values (x1/x2 lane configs). PreShoot and DeEmphasis 
>>> values
>>> are 0..7. Precode enable values are 0/1 and only applicable to HS-G6.
>>>
>>> Acked-by: Manivannan Sadhasivam <[email-masked]>
>>> Reviewed-by: Bean Huo <[email-masked]>
>>> Reviewed-by: Peter Wang <[email-masked]>
>>> Signed-off-by: Can Guo <[email-masked]>
>>> ---
>>>   .../devicetree/bindings/ufs/ufs-common.yaml   | 45 
>>> +++++++++++++++++++
>>>   1 file changed, 45 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/ufs/ufs-common.yaml 
>>> b/Documentation/devicetree/bindings/ufs/ufs-common.yaml
>>> index ed97f5682509..d90cf25adfa5 100644
>>> --- a/Documentation/devicetree/bindings/ufs/ufs-common.yaml
>>> +++ b/Documentation/devicetree/bindings/ufs/ufs-common.yaml
>>> @@ -105,6 +105,51 @@ properties:
>>>         Restricts the UFS controller to rate-a or rate-b for both TX 
>>> and
>>>         RX directions.
>>>   +  tx-precode-enable-g6:
>>> +    $ref: /schemas/types.yaml#/definitions/uint32-array
>>> +    oneOf:
>>> +      - minItems: 2
>>> +        maxItems: 2
>>> +      - minItems: 4
>>> +        maxItems: 4
>>> +    items:
>>> +      enum: [0, 1]
>>> +    description: |
>>> +      Static TX Precode enable values for HS-G6 only.
>>> +      Values are specified as per-lane tuples:
>>> +      <Host_Lane0 Device_Lane0>, [<Host_Lane1 Device_Lane1>].
>> You need to include them in any of applicable examples, otherwise
>> nothing here is validated.
> Hi Krzysztof,
>
> Thanks for the review.
>
> Since no UFS5-capable SoC binding exists upstream yet (the target SoC is
> still pre-CS), there is no vendor-specific YAML to attach the example to.
>
> Is a synthetic example directly in ufs-common.yaml OK to you?
Let me update qcom,sm8650-ufshc.yaml as it includes sm8650 and others.

Thanks,
Can Guo.
>>
>> Why values cannot be on or off? Or even better: why you cannot just list
>> all the lanes which has it enabled, assuming disabled is by default?
> Thanks for the suggestions.
>
> For the "just list enabled lanes" suggestion: precode must be configured
> independently for the Host-side TX and Device-side TX transceivers within
> the same physical lane. A lane index list alone cannot capture this
> two-dimensional per-lane state. The tuple format <Host_LaneN 
> Device_LaneN>
> is the minimal encoding that covers both.
>
> For the "on/off" suggestion: the on/off string pattern is used with
> single-value properties (e.g. LED default-state) read via
> of_property_read_string(). I am not aware of precedent for on/off as a
> string array for per-lane tuples.
>>
>>> +
>>> +patternProperties:
>>> +  "^txeq-preshoot-g[1-6]$":
>>> +    $ref: /schemas/types.yaml#/definitions/uint32-array
>>> +    oneOf:
>>> +      - minItems: 2
>>> +        maxItems: 2
>>> +      - minItems: 4
>>> +        maxItems: 4
>>> +    items:
>>> +      minimum: 0
>>> +      maximum: 7
>> What is the meaning of values? Nothing here refers to the spec, so is
>> this driver specific?
> These are not driver-specific. PreShoot and DeEmphasis are standard
> features of the MIPI M-PHY / UniPro stack. The range [0, 7] is defined
> in the UniPro specification for the relevant PA layer attributes, and 
> each
> value maps to a specific dB level as defined in the M-PHY specification.
> I will add the value-to-dB mapping table to the property descriptions 
> in v7.
>
> Thanks,
> Can Guo.
>>
>> Best regards,
>> Krzysztof
>>
>