linux-kernel - Re: [PATCH v2 1/3] dt-bindings: phy: qcom,usb-snps-femto-v2: Add phy override params bindings

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Date:   Mon, 14 Mar 2022 08:39:57 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Pavan Kondeti <quic_pkondeti@...cinc.com>
Cc:     Sandeep Maheswaram <quic_c_sanm@...cinc.com>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Wesley Cheng <wcheng@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org,
        linux-usb@...r.kernel.org, quic_ppratap@...cinc.com,
        quic_kriskura@...cinc.com
Subject: Re: [PATCH v2 1/3] dt-bindings: phy: qcom,usb-snps-femto-v2: Add phy
 override params bindings

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@...cinc.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