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

[Naresh Solanki]

Hi,

On Tue, 22 Aug 2023 at 18:47, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> On Tue, Aug 22, 2023 at 02:32:31PM +0530, Naresh Solanki wrote:
> > Hi
> >
> > On Fri, 18 Aug 2023 at 14:53, Krzysztof Kozlowski
> > <krzysztof.kozlowski@xxxxxxxxxx> wrote:
> > >
> > > On 16/08/2023 10:51, Naresh Solanki wrote:
> > > > Hi Krzysztof,
> > > >
> > > > On Tue, 15 Aug 2023 at 01:02, Krzysztof Kozlowski
> > > > <krzysztof.kozlowski@xxxxxxxxxx> wrote:
> > > >>
> > > >> On 11/08/2023 18:00, Naresh Solanki wrote:
> > > >>> Hi,
> > > >>>
> > > >>> On Tue, 8 Aug 2023 at 19:58, Conor Dooley <conor@xxxxxxxxxx> 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@xxxxxxxxxxxxx>
> > > >>>>>>>
> > > >>>>>>> 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
>
> Messy, because while it reflects physical connectivity, it doesn't reflect
> its use in the system at all. The pin may be at fixed level or left
> unconnected, but the system vendor doesn't want to give users the
> means to control output power (which would be the normal situation).
Maybe this would be better ?
infineon,svid-mode-fixed-en-pin
  description: |
    Indicate the ENABLE pin is set at fixed level or left
    unconnected(has internal pull-up) which chip in
    SVID mode.

Regards,
Naresh
>
> But then, if that is the only way to get a property accepted, so be it.
>
> Guenter