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SubjectRe: [PATCH v2 1/3] dt-bindings: phy: qcom,usb-snps-femto-v2: Add phy override params bindings
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On 14/03/2022 04:29, Pavan Kondeti wrote:
> Hi Krzysztof,
>
> On Thu, Mar 03, 2022 at 04:59:22PM +0100, Krzysztof Kozlowski wrote:
>> On 03/03/2022 07:13, Sandeep Maheswaram wrote:
>>> Add device tree bindings for SNPS phy tuning parameters.
>>>
>>> Signed-off-by: Sandeep Maheswaram <quic_c_sanm@quicinc.com>
>>> ---
>>> .../bindings/phy/qcom,usb-snps-femto-v2.yaml | 125 +++++++++++++++++++++
>>> 1 file changed, 125 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/phy/qcom,usb-snps-femto-v2.yaml b/Documentation/devicetree/bindings/phy/qcom,usb-snps-femto-v2.yaml
>>> index 0dfe691..227c097 100644
>>> --- a/Documentation/devicetree/bindings/phy/qcom,usb-snps-femto-v2.yaml
>>> +++ b/Documentation/devicetree/bindings/phy/qcom,usb-snps-femto-v2.yaml
>>> @@ -50,6 +50,131 @@ properties:
>>> vdda33-supply:
>>> description: phandle to the regulator 3.3V supply node.
>>>
>>> + qcom,hs-disconnect:
>>> + $ref: /schemas/types.yaml#/definitions/uint32
>>> + description:
>>> + This adjusts the voltage level for the threshold used to
>>> + detect a disconnect event at the host. Possible values are.
>>
>> ':', instead of full stop.
>>
>>> + 7 -> +21.56%
>>> + 6 -> +17.43%
>>> + 5 -> +13.32%
>>> + 4 -> +9.73%
>>> + 3 -> +6.3
>>> + 2 -> +3.17%
>>> + 1 -> 0, Design default%
>>
>> Use "default:" instead. Here and in other places.
>>
>>> + 0 -> -2.72%
>>
>> In current form this should be an enum... but actually current form is
>> wrong. You should not store register values in DT. What if next version
>> of hardware has a different meaning of these values?
>>
>> Instead, you should store here meaningful values, not register values.
>>
>
> Thanks for the feedback.
>
> The values in % really makes the tuning easy. People look at the eye diagram
> and decided whether to increase/decrease the margin. The absolute values
> may not be that useful. All we need is an "adjustment" here. The databook
> it self does not give any absolute values.
>
> I agree to the "enum" suggestion which we have been following for the
> qusb2 driver already.
>
> The values have not changed in the last 5 years for this hardware block, so
> defining enums for the % values would be really helpful.

I did not say you cannot store here percentages. Quite opposite - store
here the percentages. Just do not store register value. No. Please read
my comment again - meaningful values are needed.


Best regards,
Krzysztof

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