linux-kernel - Re: [PATCH v8 1/3] dt-bindings: phy: qcom,usb-snps-femto-v2: Add phy override params bindings

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Message-ID: <c8c3775c-6724-1726-7c2e-cdfb8bf71e1b@quicinc.com>
Date:   Wed, 8 Jun 2022 21:44:56 +0530
From:   Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
To:     Vinod Koul <vkoul@...nel.org>
CC:     Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Stephen Boyd <swboyd@...omium.org>,
        "Doug Anderson" <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Wesley Cheng <quic_wcheng@...cinc.com>,
        <devicetree@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-phy@...ts.infradead.org>, <quic_pkondeti@...cinc.com>,
        <quic_ppratap@...cinc.com>, <quic_vpulyala@...cinc.com>,
        Sandeep Maheswaram <quic_c_sanm@...cinc.com>
Subject: Re: [PATCH v8 1/3] dt-bindings: phy: qcom,usb-snps-femto-v2: Add phy
 override params bindings


On 6/8/2022 9:23 PM, Vinod Koul wrote:
> On 01-06-22, 12:26, Krishna Kurapati wrote:
>> From: Sandeep Maheswaram <quic_c_sanm@...cinc.com>
>>
>> Add device tree bindings for SNPS phy tuning parameters.
>>
>> Signed-off-by: Sandeep Maheswaram <quic_c_sanm@...cinc.com>
>> Signed-off-by: Krishna Kurapati <quic_kriskura@...cinc.com>
>> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> ---
>>   .../bindings/phy/qcom,usb-snps-femto-v2.yaml       | 96 ++++++++++++++++++++++
>>   1 file changed, 96 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 1ce251d..daeeb04 100644
>> --- a/Documentation/devicetree/bindings/phy/qcom,usb-snps-femto-v2.yaml
>> +++ b/Documentation/devicetree/bindings/phy/qcom,usb-snps-femto-v2.yaml
>> @@ -53,6 +53,102 @@ properties:
>>     vdda33-supply:
>>       description: phandle to the regulator 3.3V supply node.
>>   
>> +  qcom,hs-disconnect-bp:
>> +    description:
>> +      This adjusts the voltage level for the threshold used to
>> +      detect a disconnect event at the host. Possible values are.
>> +      The values defined are in multiples of basis points (1bp = 0.01%).
>> +      The hardware accepts only discrete values. The value closest to the
>> +      provided input will be chosen as the override value for this param.
>> +    minimum: -272
>> +    maximum: 2156
>> +
>> +  qcom,squelch-detector-bp:
>> +    description:
>> +      This adjusts the voltage level for the threshold used to
>> +      detect valid high-speed data.
>> +      The values defined are in multiples of basis points (1bp = 0.01%).
>> +      The hardware accepts only discrete values. The value closest to the
>> +      provided input will be chosen as the override value for this param.
>> +    minimum: -2090
>> +    maximum: 1590
>> +
>> +  qcom,hs-amplitude-bp:
>> +    description:
>> +      This adjusts the high-speed DC level voltage.
>> +      The values defined are in multiples of basis points (1bp = 0.01%).
>> +      The hardware accepts only discrete values. The value closest to the
>> +      provided input will be chosen as the override value for this param.
>> +    minimum: -660
>> +    maximum: 2670
>> +
>> +  qcom,pre-emphasis-duration-bp:
>> +    description:
>> +      This signal controls the duration for which the
>> +      HS pre-emphasis current is sourced onto DP<#> or DM<#>.
>> +      The HS Transmitter pre-emphasis duration is defined in terms of
>> +      unit amounts. One unit of pre-emphasis duration is approximately
>> +      650 ps and is defined as 1X pre-emphasis duration.
>> +      The values defined are in multiples of basis points (1bp = 0.01%).
>> +      The hardware accepts only discrete values. The value closest to the
>> +      provided input will be chosen as the override value for this param.
>> +    minimum: 10000
>> +    maximum: 20000
>> +
>> +  qcom,pre-emphasis-amplitude-bp:
>> +    description:
>> +      This signal controls the amount of current sourced to
>> +      DP<#> and DM<#> after a J-to-K or K-to-J transition.
>> +      The HS Transmitter pre-emphasis current is defined in terms of unit
>> +      amounts. One unit amount is approximately 2 mA and is defined as
>> +      1X pre-emphasis current.
>> +      The values defined are in multiples of basis points (1bp = 0.01%).
>> +      The hardware accepts only discrete values. The value closest to the
>> +      provided input will be chosen as the override value for this param.
>> +    minimum: 10000
>> +    maximum: 40000
>> +
>> +  qcom,hs-rise-fall-time-bp:
>> +    description:
>> +      This adjusts the rise/fall times of the high-speed waveform.
>> +      The values defined are in multiples of basis points (1bp = 0.01%).
>> +      The hardware accepts only discrete values. The value closest to the
>> +      provided input will be chosen as the override value for this param.
>> +    minimum: -4100
>> +    maximum: 5430
>> +
>> +  qcom,hs-crossover-voltage-microvolt:
>> +    description:
>> +      This adjusts the voltage at which the DP<#> and DM<#>
>> +      signals cross while transmitting in HS mode.
>> +      The values defined are in milli volts. The hardware accepts only
>> +      discrete values. The value closest to the provided input will be
>> +      chosen as the override value for this param.
>> +    minimum: -31000
>> +    maximum: 28000
>> +
>> +  qcom,hs-output-impedance-micro-ohms:
>> +    description:
>> +      In some applications, there can be significant series resistance
>> +      on the D+ and D- paths between the transceiver and cable. This adjusts
>> +      the driver source impedance to compensate for added series
>> +      resistance on the USB. The values defined are in milli ohms.
>> +      The hardware accepts only discrete values. The value closest to the
>> +      provided input will be chosen as the override value for this param.
>> +    minimum: -2300000
>> +    maximum: 6100000
>> +
>> +  qcom,ls-fs-output-impedance-bp:
>> +    description:
>> +      This adjusts the low- and full-speed single-ended source
>> +      impedance while driving high. The following adjustment values are based
>> +      on nominal process, voltage, and temperature.
>> +      The values defined are in multiples of basis points (1bp = 0.01%).
>> +      The hardware accepts only discrete values. The value closest to the
>> +      provided input will be chosen as the override value for this param.
>> +    minimum: -1053
>> +    maximum: 1310
> do we need all these values in DT, till now we have these in driver..
> what is the reasoning to add these in DT instead?

Hi Vinod,

   The patch series started out as you mentioned. We used to have phy 
tune register values passed from dT to driver and written to respective 
registers in the driver code.

But it was later suggested not to pass register values from dT. Instead 
define the meaningful properties that make up the phy tuning parameters 
and pass their values from dT. The driver code is supposed to convert 
these values and map them to required register values. This is why we 
had to come up with these parameters and declare them in bindings and dT.

More info regarding the discussion at : 
https://lore.kernel.org/linux-usb/b45b3b7e-e1c0-79b6-81c0-53c70427dd10@canonical.com/


Regards,

Krishna,