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

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Date:   Fri, 18 May 2018 07:29:04 +0000
From:   Amelie DELAUNAY <amelie.delaunay@...com>
To:     Lee Jones <lee.jones@...aro.org>
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 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 ? :)

Thanks,
Amelie