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

From: Can Guo <[email-masked]>
Date: Sun, 31 May 2026 12:48:29 +0800

On 5/31/2026 9:41 AM, Can Guo wrote:
>
>
> On 5/31/2026 1:33 AM, Krzysztof Kozlowski wrote:
>> On 30/05/2026 14:45, 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
>> I would imagine cover letter or commit msg would briefly mention that.
> Thanks for the clarification. Will do.
>>
>>> 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?
>> Skip example in such case.
>>
>>>> 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.
>> Again, why do you need to encode '0'?
> The tuple is still needed because Precoding is configured per 
> transmitter-receiver pair,
> so each lane has two independent states:
> - Host_TX -> Device_RX
> - Device_TX -> Host_RX
> A lane-only enabled list cannot represent directional combinations 
> like lane0 =
> (on, off) vs (off, on).
How about we split into two properties, something like below?
tx-precode-enable-g6-host-lanes = <0 1>
tx-precode-enable-g6-device-lanes = <1>

Only listed lanes are enabled; unlisted lanes are disabled by default.

Are you OK with this approach?

Thanks,
Can Guo.
>>
>>> 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.
>> git grep string-array. Plenty of precedents.
> I will keep the per-lane tuple model but switch tx-precode-enable-g6 
> from 0/1 to
> "on"/"off" (string array) in v7.
>
> Thanks,
> Can Guo.
>>
>> Best regards,
>> Krzysztof
>