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 20:45:27 +0800

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?
>
> 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