linux-kernel - Re: [PATCH v6 02/13] dt-bindings: mfd: Add bindings for sl28cpld

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Date:   Tue, 28 Jul 2020 10:20:16 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Michael Walle <michael@...le.cc>
Cc:     linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Jean Delvare <jdelvare@...e.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <maz@...nel.org>, Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Pavel Machek <pavel@....cz>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v6 02/13] dt-bindings: mfd: Add bindings for sl28cpld

On Tue, 28 Jul 2020, Michael Walle wrote:

> Am 2020-07-28 10:56, schrieb Lee Jones:
> > > > > > > +$id: http://devicetree.org/schemas/mfd/kontron,sl28cpld.yaml#
> > > > > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > > > > +
> > > > > > > +title: Kontron's sl28cpld board management controller
> > > > > >
> > > > > > "S128CPLD" ?
> > > > >
> > > > > still not, its sl28cpld, think of a project/code name, not the product
> > > > > appended with CPLD.
> > > > >
> > > > > > "Board Management Controller (BMC)" ?
> > > > >
> > > > > sounds like IPMI, which I wanted to avoid.
> > > >
> > > > Is there a datasheet?
> > > 
> > > No there isn't.
> > 
> > Then what are you working from?
> 
> Ok, there is no public datasheet. If that wasn't clear before, I'm working
> for that company that also implemented that CPLD.

No, that wasn't clear.  You said there was no datasheet.

> > > > > > > +maintainers:
> > > > > > > +  - Michael Walle <michael@...le.cc>
> > > > > > > +
> > > > > > > +description: |
> > > > > > > +  The board management controller may contain different IP blocks
> > > > > > > like
> > > > > > > +  watchdog, fan monitoring, PWM controller, interrupt controller
> > > > > > > and a
> > > > > > > +  GPIO controller.
> > > > > > > +
> > > > > > > +properties:
> > > > > > > +  compatible:
> > > > > > > +    const: kontron,sl28cpld-r1
> > > > > >
> > > > > > We don't usually code revision numbers in compatible strings.
> > > > > >
> > > > > > Is there any way to pull this from the H/W?
> > > > >
> > > > > No, unfortunately you can't. And I really want to keep that, in case
> > > > > in the future there are some backwards incompatible changes.
> > > >
> > > > Rob,
> > > >
> > > > I know you reviewed this already, but you can give your opinion on
> > > > this specifically please?  I know that we have pushed back on this in
> > > > the past.
> > > 
> > > Oh, come one. That is an arbitrary string. "sl28cpld-r1" is the first
> > > implementation of this. A future "sl28cpld-r2" might look completely
> > > different and might not suite the simple MFD at all. "sl28cpld" is
> > > a made up name - as "sl28cpld-r1" is, too.
> > 
> > Well that sounds bogus for a start.  I guess that's one of the
> > problems with trying to support programmable H/W in S/W.
> 
> What sounds bogus? That we name the implementation sl28cpld?
> How is that different to like adt7411? Its just a name made up by
> the vendor. So if there is a new version of the adt7411 the vendor 
> might name it adt7412.

Using an arbitrary string as a compatible would be bogus.

So here 'sl28cpld' is the device name, so it's not actually
arbitrary.  That's a good start.

> We name it sl28cpld-r2. So what is the problem here?

Do you though?  So 'sl28cpld-r1' is the name of the device?  The name
that is quoted from the (private) datasheet?  Because looking at the
implementation and going by the conversation, it sounds as though
you-re only adding the '-r1' piece to the compatible string for
revision identification.  Which if true, is not usually allowed and
warrants intervention by Rob.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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