linux-kernel - Re: [PATCH 1/5] dt-bindings: pinctrl: document the STMFX pinctrl bindings

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Date:   Fri, 18 May 2018 14:52:37 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Amelie DELAUNAY <amelie.delaunay@...com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/5] dt-bindings: pinctrl: document the STMFX pinctrl
 bindings

On Fri, 18 May 2018, Amelie DELAUNAY wrote:

> On 05/17/2018 08:36 AM, Lee Jones wrote:
> > On Wed, 16 May 2018, Amelie DELAUNAY wrote:
> > 
> >>
> >>
> >> On 05/16/2018 04:20 PM, Linus Walleij wrote:
> >>> On Wed, May 9, 2018 at 9:56 AM, Amelie DELAUNAY <amelie.delaunay@...com> wrote:
> >>>
> >>>> Indeed, stmfx has other functions than GPIO. But, after comments done
> >>>> here: [1] and there: [2], it has been decided to move MFD parent/GPIO
> >>>> child drivers into a single PINCTRL/GPIO driver because of the following
> >>>> reasons:
> >>>> - Other stmfx functions (IDD measurement and TouchScreen controller) are
> >>>> not used on any of the boards using an stmfx and supported by Linux, so
> >>>> no way to test these functions, and no need to maintain them while they
> >>>> are not being used.
> >>>> - But, in the case a new board will use more than GPIO function on
> >>>> stmfx, the actual implementation allow to easily extract common init
> >>>> part of stmfx and put it in an MFD driver.
> >>>>
> >>>> So I could remove gpio sub-node and put its contents in stmfx node and
> >>>> keep single PINCTRL/GPIO driver for the time being.
> >>>> Please advise,
> >>>
> >>> I would normally advice to use the right modeling from the start, create
> >>> the MFD driver and spawn the devices from there. It is confusing
> >>> if the layout of the driver(s) doesn't really match the layout of the
> >>> hardware.
> >>>
> >>> I understand that it is a pain to write new MFD drivers to get your
> >>> things going and it would be "nice to get this working really quick
> >>> now" but in my experience it is better to do it right from the start.
> >>>
> >>
> >> Hi Linus,
> >>
> >> Thanks for your advice. I understand the point.
> >> So, the right modeling would be to:
> >> - create an MFD driver with the common init part of stmfx
> >> - remove all common init part of stmfx-pinctrl driver and keep only all
> >> gpio/pinctrl functions.
> >>
> >> I will not develop the other stmfx functions (IDD measurement driver and
> >> TouchScreen controller driver) because, as explained ealier, they are
> >> not used on any of the boards using an stmfx and supported by Linux, so
> >> no way to test these functions, and no need to maintain them while they
> >> are not being used.
> >>
> >> Lee, are you OK with that ?
> > 
> > I missed a lot of this conversation I think, but from what I've read,
> > it sounds fine.
> > 
> 
> I summarize the situation:
> - I still don't have an official datasheet for STMFX device which could 
> justify the use of an MFD driver;
> - the MFD driver will contain the STMFX chip initialization stuff such 
> as regmap initialization (regmap structure will be shared with the 
> child), chip initialization, global interrupt management;
> - there will be only one child (GPIO/PINCTRL node) for the time being.
> 
> So, is "MFD driver + GPIO/PINCTRL driver" the right modeling, and does 
> it still sound fine after this summary ? :)

It is starting to sound like there will only ever be one child device,
which starts to cross the line into "this is not an MFD" (M = Multi)
territory.

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