linux-kernel - Re: [PATCH v3 1/3] dt-bindings: hwmon: Add Infineon TDA38640

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Date:   Tue, 22 Aug 2023 14:32:31 +0530
From:   Naresh Solanki <naresh.solanki@...ements.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Conor Dooley <conor@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Jean Delvare <jdelvare@...e.com>,
        krzysztof.kozlowski+dt@...aro.org,
        Rob Herring <robh+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        linux-hwmon@...r.kernel.org,
        Patrick Rudolph <patrick.rudolph@...ements.com>,
        Rob Herring <robh@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] dt-bindings: hwmon: Add Infineon TDA38640

Hi

On Fri, 18 Aug 2023 at 14:53, Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> wrote:
>
> On 16/08/2023 10:51, Naresh Solanki wrote:
> > Hi Krzysztof,
> >
> > On Tue, 15 Aug 2023 at 01:02, Krzysztof Kozlowski
> > <krzysztof.kozlowski@...aro.org> wrote:
> >>
> >> On 11/08/2023 18:00, Naresh Solanki wrote:
> >>> Hi,
> >>>
> >>> On Tue, 8 Aug 2023 at 19:58, Conor Dooley <conor@...nel.org> wrote:
> >>>>
> >>>> On Tue, Aug 08, 2023 at 07:10:08AM -0700, Guenter Roeck wrote:
> >>>>> On 8/8/23 04:46, Conor Dooley wrote:
> >>>>>> On Wed, Aug 02, 2023 at 09:31:51PM +0200, Naresh Solanki wrote:
> >>>>>>> From: Patrick Rudolph <patrick.rudolph@...ements.com>
> >>>>>>>
> >>>>>>> The TDA38640 chip has different output control mechanisms depending on
> >>>>>>> its mode of operation. When the chip is in SVID mode, only
> >>>>>>> hardware-based output control is supported via ENABLE pin. However, when
> >>>>>>> it operates in PMBus mode, software control works perfectly.
> >>>>>>>
> >>>>>>> To enable software control as a workaround in SVID mode, add the DT
> >>>>>>> property 'infineon,en-svid-control'. This property will enable the
> >>>>>>> workaround, which utilizes ENABLE pin polarity flipping for output when
> >>>>>>> the chip is in SVID mode.
> >>>>>>
> >>>>>> Why do you need a custom property for this? How come it is not possible
> >>>>>> to determine what bus you are on?
> >>>>>>
> >>>>>
> >>>>> That is not the point. Yes, it can be detected if the control method is
> >>>>> PMBus or SVID. However, in SVID mode, SVID is supposed to control the
> >>>>> output, not PMBUs. This is bypassed by controlling the polarity of the
> >>>>> (physical) output enable signal. We do _not_ want this enabled automatically
> >>>>> in SVID mode. Its side effects on random boards using this chip are unknown.
> >>>>> Thus, this needs a property which specifically enables this functionality
> >>>>> for users who _really_ need to use it and (hopefully) know what they are
> >>>>> doing.
> >>>>
> >>>> Hmm, reading this it makes a lot more sense why this is a property - I
> >>>> guess I just struggled to understand the commit message here,
> >>>> particularly what the benefit of using the workaround is. I'm still
> >>>> having difficulty parsing the commit & property text though - its
> >>>> unclear to me when you would need to use it - so I will stay out
> >>>> of the way & let Rob or Krzysztof handle things.
> >>>
> >>> To provide context, my system employs a unique power sequence
> >>> strategy utilizing a BMC (Baseboard Management Controller),
> >>> rendering the reliance on the ENABLE pin unnecessary.
> >>> In this configuration, the ENABLE pin is grounded in the hardware.
> >>> While most regulators facilitate PMBus Operation for output control,
> >>> the TDA38640 chip, when in SVID mode, is constrained by the
> >>> ENABLE pin to align with Intel specifications.
> >>> My communication with Infineon confirmed that the recommended
> >>> approach is to invert the Enable Pin for my use case.
> >>>
> >>> Since this is not typically the use case for most setup & hence DT property
> >>> is must for enabling the special case.
> >>>
> >>> For further insight into my setup's power sequence strategy, you can
> >>> refer to the following link: https://github.com/9elements/pwrseqd
> >>>
> >>
> >> This justifies to me the property, but still you described desired
> >> driver behavior, not the hardware characteristic. Don't describe what
> >> you want to control, but describe the entire system.
> > I guess by entire system you mean how the regulators(including
> > TDA38640) connected & operated in our setup ?
>
> I mean, property name and description should say what is the
> characteristic of the hardware/firmware/entire system.
Based on your feedback, will update to below:
infineon,fixed-level-en-pin:
    description: |
      Indicate the ENABLE pin is set at fixed level or left
      unconnected(has internal pull-up).
    type: boolean
>
>
> Best regards,
> Krzysztof
>