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

Paul Cercueil
2020-04-18T17:25:33Z

Hi Jonathan,

Le sam. 18 avril 2020 à 15:22, Jonathan Cameron <jic23@kernel.org> a
écrit :
> On Sat, 18 Apr 2020 15:24:58 +0200
> Paul Cercueil <paul@crapouillou.net> wrote:
>
>> Le sam. 18 avril 2020 à 15:42, Andy Shevchenko
>> <andy.shevchenko@gmail.com> a écrit :
>> > On Sat, Apr 18, 2020 at 3:10 PM Paul Cercueil
>> <paul@crapouillou.net>
>> > wrote:
>> >> Le sam. 18 avril 2020 à 14:57, Andy Shevchenko
>> >> <andy.shevchenko@gmail.com> a écrit :
>> >> > On Sat, Apr 18, 2020 at 1:48 AM Paul Cercueil
>> >> <paul@crapouillou.net>
>> >> > wrote:
>> >> >> Le sam. 18 avril 2020 à 0:49, Andy Shevchenko
>> >> >> <andy.shevchenko@gmail.com> a écrit :
>> >> >> > On Sat, Apr 18, 2020 at 12:24 AM Paul Cercueil
>> >> >> <paul@crapouillou.net>
>> >> >> > wrote:
>> >> >> >> Le sam. 18 avril 2020 à 0:10, Andy Shevchenko
>> >> >> >> <andy.shevchenko@gmail.com> a écrit :
>> >> >> >> > On Fri, Apr 17, 2020 at 11:21 PM Artur Rojek
>> >> >> >> <contact@artur-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.
>>
>> This is how the platform devices were instanciated on JZ4740 before
>> we
>> 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?
>> >>
>> >> 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.
>>
>> The fact that it was designed for something else doesn't mean it
>> can't
>> be used.
>>
>> Anyway, this discussion is pointless. I don't think anybody would
>> want
>> 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
>> >> 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.
>>
>> 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
>> done here.
>>
>> > 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.
>>
>> And how is unconditionally compiling the of_match_table make it
>> magically probe from ACPI, without a acpi_match_table?
>>
>> -Paul
>
> Look up PRP0001 ACPI ID. Magic trick ;)
>
> https://www.kernel.org/doc/html/latest/firmware-guide/acpi/enumeration.html?highlight=PRP0001
>
> It allows you to define an ACPI device in DSDT that is instantiated
> from what is effectively the DT binding including the id table.

So what you're saying, is that the OF table should be present, even
though CONFIG_OF is not set, just in case it is probed from ACPI?

-Paul