linux-kernel - Re: [RESEND PATCH v5 5/5] input: joystick: Add ADC attached joystick driver.

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Message-ID: <CAHp75VdE=xHi8Kn=nZiH+shHvS6O2pc6W=FCs_VwrJq6Bfwx7w@mail.gmail.com>
Date:   Sat, 18 Apr 2020 15:42:16 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     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 5/5] input: joystick: Add ADC attached joystick driver.

On Sat, Apr 18, 2020 at 3:10 PM Paul Cercueil <paul@...pouillou.net> wrote:
> Le sam. 18 avril 2020 à 14:57, Andy Shevchenko
> <andy.shevchenko@...il.com> a écrit :
> > On Sat, Apr 18, 2020 at 1:48 AM Paul Cercueil <paul@...pouillou.net>
> > wrote:
> >>  Le sam. 18 avril 2020 à 0:49, Andy Shevchenko
> >>  <andy.shevchenko@...il.com> a écrit :
> >>  > On Sat, Apr 18, 2020 at 12:24 AM Paul Cercueil
> >> <paul@...pouillou.net>
> >>  > wrote:
> >>  >>  Le sam. 18 avril 2020 à 0:10, Andy Shevchenko
> >>  >>  <andy.shevchenko@...il.com> a écrit :
> >>  >>  > On Fri, Apr 17, 2020 at 11:21 PM Artur Rojek
> >>  >> <contact@...ur-rojek.eu>
> >>  >>  > wrote:

...

> >>  >>  >>  +#include <linux/of.h>
> >>  >>  >
> >>  >>  > Do you really need this? (See below as well)
> >>  >
> >>  >>  >>  +static const struct of_device_id adc_joystick_of_match[] =
> >> {
> >>  >>  >>  +       { .compatible = "adc-joystick", },
> >>  >>  >>  +       { },
> >>  >>  >>  +};
> >>  >>  >>  +MODULE_DEVICE_TABLE(of, adc_joystick_of_match);
> >>  >>  >>  +
> >>  >>  >>  +static struct platform_driver adc_joystick_driver = {
> >>  >>  >>  +       .driver = {
> >>  >>  >>  +               .name = "adc-joystick",
> >>  >>  >
> >>  >>  >>  +               .of_match_table =
> >>  >>  >> of_match_ptr(adc_joystick_of_match),
> >>  >>  >
> >>  >>  > Drop this a bit harmful of_match_ptr() macro. It should go
> >> with
> >>  >> ugly
> >>  >>  > #ifdeffery. Here you simple introduced a compiler warning.
> >>  >>
> >>  >>  I assume you mean #ifdef around the of_device_id + module table
> >>  >> macro?
> >>  >
> >>  > Yes.
> >>  >
> >>  >>  > On top of that, you are using device property API, OF use in
> >> this
> >>  >> case
> >>  >>  > is contradictory (at lest to some extend).
> >>  >>
> >>  >>  I don't see why. The fact that the driver can work when probed
> >> from
> >>  >>  platform code
> >>  >
> >>  > Ha-ha, tell me how. I would like to be very surprised.
> >>
> >>  iio_map_array_register(),
> >>  pinctrl_register_mappings(),
> >>  platform_add_devices(),
> >>
> >>  you're welcome.
> >
> > I think above has no relation to what I'm talking about.
>
> Yes it does. It allows you to map the IIO channels, set the pinctrl
> configurations and register a device from platform code instead of
> devicetree.

I'm not talking about other drivers, I'm talking about this driver and
how it will be instantiated. Above, according to the code, can't be
comprehensive to fulfill this.

> > How *this* driver can work as a platform instantiated one?
> > We seems have a conceptual misunderstanding here.
> >
> > For example, how can probe of this driver not fail, if it is not
> > backed by a DT/ACPI properties?
>
> platform_device_add_properties().

Yes, I waited for this. And seems you don't understand the (scope of)
API, you are trying to insist this driver can be used as a platform
one.
Sorry, I must to disappoint you, it can't. Above interface is created
solely for quirks to support (broken) DT/ACPI tables. It's not
supposed to be used as a main source for the device properties.

> >>  >>  doesn't mean that it shouldn't have a table to probe
> >>  >>  from devicetree.
> >>  >
> >>  > I didn't get what you are talking about here. The idea of
> >> _unified_
> >>  > device property API is to get rid of OF-centric code in favour of
> >> more
> >>  > generic approach. Mixing those two can be done only in specific
> >> cases
> >>  > (here is not the one).
> >>
> >>  And how are we mixing those two here? The only OF-centric thing
> >> here is
> >>  the device table, which is required if we want the driver to probe
> >> from
> >>  devicetree.
> >
> > Table is fine(JFYI the types and sections are defined outside of OF
> > stuff, though being [heavily] used by it) , API (of_match_ptr() macro
> > use) is not.
>
> Sorry, but that's just stupid. Please have a look at how of_match_ptr()
> macro is defined in <linux/of.h>.

Call it whatever you want, but above code is broken.
It needs either of:
- ugly ifdeffery
- dropping of_match_ptr()
- explicit dependence to OF

My choice is second one. Because it makes code better and allows also
ACPI to use this driver (usually) without changes.

-- 
With Best Regards,
Andy Shevchenko