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

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Date:   Tue, 8 Aug 2023 15:28:10 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Naresh Solanki <naresh.solanki@...ements.com>,
        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

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.

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