linux-kernel - Re: [RESEND PATCH v5 3/5] IIO: Ingenic JZ47xx: Add touchscreen mode.

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Date:   Sun, 19 Apr 2020 15:23:36 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Artur Rojek <contact@...ur-rojek.eu>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Cameron <jic23@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>,
        linux-input <linux-input@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH v5 3/5] IIO: Ingenic JZ47xx: Add touchscreen mode.

Hi Ezequiel,


Le dim. 19 avril 2020 à 9:54, Ezequiel Garcia 
<ezequiel@...guardiasur.com.ar> a écrit :
> On Fri, 17 Apr 2020 at 18:54, Andy Shevchenko 
> <andy.shevchenko@...il.com> wrote:
>> 
>>  On Sat, Apr 18, 2020 at 12:45 AM Paul Cercueil 
>> <paul@...pouillou.net> wrote:
>>  > Le sam. 18 avril 2020 à 0:42, Andy Shevchenko
>>  > <andy.shevchenko@...il.com> a écrit :
>>  > > On Sat, Apr 18, 2020 at 12:18 AM Paul Cercueil 
>> <paul@...pouillou.net>
>>  > > wrote:
>>  > >>  Le sam. 18 avril 2020 à 0:13, Andy Shevchenko
>>  > >>  <andy.shevchenko@...il.com> a écrit :
>>  > >>  > On Sat, Apr 18, 2020 at 12:05 AM Paul Cercueil
>>  > >> <paul@...pouillou.net>
>>  > >>  > wrote:
>>  > >>  >>  Le ven. 17 avril 2020 à 23:59, Andy Shevchenko
>>  > >>  >>  <andy.shevchenko@...il.com> a écrit :
>>  > >>  >>  > On Fri, Apr 17, 2020 at 11:21 PM Artur Rojek
>>  > >>  >> <contact@...ur-rojek.eu>
>>  > >>  >>  > wrote:
>>  > >>  >
>>  > >>  > ...
>>  > >>  >
>>  > >>  >>  >>  +       irq = platform_get_irq(pdev, 0);
>>  > >>  >>  >
>>  > >>  >>  > Before it worked w/o IRQ, here is a regression you 
>> introduced.
>>  > >>  >>
>>  > >>  >>  Before it simply did not need the IRQ, which is provided 
>> by the
>>  > >>  >>  devicetree anyway. No regression here.
>>  > >>  >
>>  > >>  > Does it work without IRQ? Or it was a dead code till now?
>>  > >>  > For me it's clear regression. Otherwise something is really 
>> wrong
>>  > >> in a
>>  > >>  > process of development of this driver.
>>  > >>
>>  > >>  Nothing wrong here. The IRQ was not used by the driver for the
>>  > >>  functionality it provided before. It is required now to 
>> support the
>>  > >>  touchscreen channels.
>>  > >
>>  > > This is exactly what's wrong.
>>  > > Previous DTS for my (hypothetical) case has no IRQ defined. 
>> Everything
>>  > > works, right?
>>  > > Now, due to this change it breaks my setup. Don't you see the 
>> problem?
>>  >
>>  > The IRQ has been provided by every concerned DTS file since the
>>  > introduction of this driver and the related bindings, even though 
>> it
>>  > was not used by the driver.
>> 
>>  Can you speak for all possible DTSs/DTBs in the wild?
>>  Okay, in any case it will be problem of maintainers and yours if
>>  somebody complains.
>>  I'm not going to push this anyway -- your choice.
>> 
>>  But I see a (potential) regression.
>> 
> 
> So, there are a few things to keep in mind here.
> 
> Let's abstract ourselves from this specific driver
> for a minute.
> 
> First, and just as Andy pointed out, we can never be fully
> sure about DTBs out there. These could be out of tree,
> so out of our control. By introducing a new requirement
> we break them, which may be seen as a regression.
> 
> Second, the interrupt is not required as per
> current mainline bindings/iio/adc/ingenic,adc.txt,
> so it is perfectly legal for users to not have an interrupt
> specified.
> 
> Now, back to this case, I think we can get away with this
> change, provided this hardware is not that widespread
> among developers/users that follow upstream closely.
> 
> I suspect anyone developing a serious platform
> with this SoC is most likely using some vendor kernel.
> 
> If that is not the case, i.e. if you have users _actually_
> using this upstream driver, then we should consider
> making the interrupt optional instead of required.
> 
> Or we can also just break it and hope nobody
> complaints.

The vast majority of Ingenic devices running Linux use a 3.x kernel 
with a lot of patches on top. These kernels don't support devicetree. 
So there is no problem with legacy devicetree files: there are no 
legacy devicetree files.

Of the few Ingenic devices running mainline kernels, all of them with 
an ADC node in the devicetree have the 'interrupts' property specified, 
out-of-tree or in-tree.

As the informal Ingenic SoCs maintainer I'm pretty aware of these 
things, and I can assure that we're not breaking anything. The only 
thing broken is the documentation which doesn't specify that the 
'interrupts' property is required.

> BTW, this series looks great and I'm happy
> to see JZ47xx activity :-)
> 
> Arthur: perhaps you can consider converting the txt dt binding
> to yaml?

That would be great.

-Paul