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

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Date:   Fri, 18 May 2018 15:13:26 +0000
From:   Amelie DELAUNAY <amelie.delaunay@...com>
To:     Lee Jones <lee.jones@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>
CC:     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 05/18/2018 03:52 PM, Lee Jones wrote:
> 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.
> 

... for the time being. So, Linus, Lee, is it possible to find common 
ground ?