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Date:   Sat, 18 Apr 2020 15:24:58 +0200
From:   Paul Cercueil <paul@crapouillou.net>
Subject: Re: [RESEND PATCH v5 5/5] input: joystick: Add ADC attached joystick
 driver.
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     Artur Rojek <contact@artur-rojek.eu>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Jonathan Cameron <jic23@kernel.org>,
        Heiko Stuebner <heiko@sntech.de>,
        linux-input <linux-input@vger.kernel.org>,
        devicetree <devicetree@vger.kernel.org>,
        linux-iio <linux-iio@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Le sam. 18 avril 2020 =E0 15:42, Andy Shevchenko=20
<andy.shevchenko@gmail.com> a =E9crit :
> On Sat, Apr 18, 2020 at 3:10 PM Paul Cercueil <paul@crapouillou.net>=20
> wrote:
>>  Le sam. 18 avril 2020 =E0 14:57, Andy Shevchenko
>>  <andy.shevchenko@gmail.com> a =E9crit :
>>  > On Sat, Apr 18, 2020 at 1:48 AM Paul Cercueil=20
>> <paul@crapouillou.net>
>>  > wrote:
>>  >>  Le sam. 18 avril 2020 =E0 0:49, Andy Shevchenko
>>  >>  <andy.shevchenko@gmail.com> a =E9crit :
>>  >>  > On Sat, Apr 18, 2020 at 12:24 AM Paul Cercueil
>>  >> <paul@crapouillou.net>
>>  >>  > wrote:
>>  >>  >>  Le sam. 18 avril 2020 =E0 0:10, Andy Shevchenko
>>  >>  >>  <andy.shevchenko@gmail.com> a =E9crit :
>>  >>  >>  > On Fri, Apr 17, 2020 at 11:21 PM Artur Rojek
>>  >>  >> <contact@artur-rojek.eu>
>>  >>  >>  > wrote:
>=20
> ...
>=20
>>  >>  >>  >>  +#include <linux/of.h>
>>  >>  >>  >
>>  >>  >>  > Do you really need this? (See below as well)
>>  >>  >
>>  >>  >>  >>  +static const struct of_device_id=20
>> adc_joystick_of_match[] =3D
>>  >> {
>>  >>  >>  >>  +       { .compatible =3D "adc-joystick", },
>>  >>  >>  >>  +       { },
>>  >>  >>  >>  +};
>>  >>  >>  >>  +MODULE_DEVICE_TABLE(of, adc_joystick_of_match);
>>  >>  >>  >>  +
>>  >>  >>  >>  +static struct platform_driver adc_joystick_driver =3D {
>>  >>  >>  >>  +       .driver =3D {
>>  >>  >>  >>  +               .name =3D "adc-joystick",
>>  >>  >>  >
>>  >>  >>  >>  +               .of_match_table =3D
>>  >>  >>  >> 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=20
>> table
>>  >>  >> macro?
>>  >>  >
>>  >>  > Yes.
>>  >>  >
>>  >>  >>  > On top of that, you are using device property API, OF use=20
>> in
>>  >> this
>>  >>  >> case
>>  >>  >>  > is contradictory (at lest to some extend).
>>  >>  >>
>>  >>  >>  I don't see why. The fact that the driver can work when=20
>> 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.
>>=20
>>  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.
>=20
> 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.

This is how the platform devices were instanciated on JZ4740 before we=20
switched everything to devicetree.

>>  > 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?
>>=20
>>  platform_device_add_properties().
>=20
> 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.

The fact that it was designed for something else doesn't mean it can't=20
be used.

Anyway, this discussion is pointless. I don't think anybody would want=20
to do that.

>>  >>  >>  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=20
>> favour of
>>  >> more
>>  >>  > generic approach. Mixing those two can be done only in=20
>> 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=20
>> probe
>>  >> from
>>  >>  devicetree.
>>  >
>>  > Table is fine(JFYI the types and sections are defined outside of=20
>> OF
>>  > stuff, though being [heavily] used by it) , API (of_match_ptr()=20
>> macro
>>  > use) is not.
>>=20
>>  Sorry, but that's just stupid. Please have a look at how=20
>> of_match_ptr()
>>  macro is defined in <linux/of.h>.
>=20
> Call it whatever you want, but above code is broken.

of_match_ptr() is basically defined like this:

#ifdef CONFIG_OF
#define of_match_ptr(x) (x)
#else
#define of_match_ptr(x) NULL
#endif

So please, enlighten me, tell me what is so wrong about what's being=20
done here.

> It needs either of:
> - ugly ifdeffery
> - dropping of_match_ptr()
> - explicit dependence to OF
>=20
> My choice is second one. Because it makes code better and allows also
> ACPI to use this driver (usually) without changes.

And how is unconditionally compiling the of_match_table make it=20
magically probe from ACPI, without a acpi_match_table?

-Paul