Re: [PATCH v7 0/4] Extend device_get_match_data() to struct bus_type

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Biju Das <biju.das.jz@bp.renesas.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Jonathan Cameron <jic23@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Peter Rosin <peda@axentia.se>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Daniel Scally <djrscally@gmail.com>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Sakari Ailus <sakari.ailus@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	Andi Shyti <andi.shyti@kernel.org>, Wolfram Sang <wsa@kernel.org>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	"linux-rtc@vger.kernel.org" <linux-rtc@vger.kernel.org>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
	"linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
	"linux-renesas-soc@vger.kernel.org" 
	<linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH v7 0/4] Extend device_get_match_data() to struct bus_type
Date: Mon, 14 Aug 2023 15:12:24 +0200	[thread overview]
Message-ID: <CAMuHMdU6LhvnZ5FE_3BxyH7reVi69Rjcircquk=jYZ6-j3cqug@mail.gmail.com> (raw)
In-Reply-To: <OS0PR01MB5922E09340CDCFF54A9A6CBA8610A@OS0PR01MB5922.jpnprd01.prod.outlook.com>

Hi Biju,

On Fri, Aug 11, 2023 at 4:46 PM Biju Das <biju.das.jz@bp.renesas.com> wrote:
> > Subject: Re: [PATCH v7 0/4] Extend device_get_match_data() to struct
> > bus_type
> >
> > On Fri, Aug 11, 2023 at 01:27:36PM +0000, Biju Das wrote:
> > > > On Thu, Aug 10, 2023 at 09:05:10AM +0000, Biju Das wrote:
> >
> > ...
> >
> > > > I'm good with this approach, but make sure you checked the whole
> > > > kernel source tree for a such.
> > >
> > > Checking against 16 is too short I guess??
> > >
> > > drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h has 18 enums.
> >
> > So, what does prevent us from moving that tables to use pointers?
>
> I think that will lead to ABI breakage(client->name vs id->name)
>
>         match = device_get_match_data(&client->dev);
>         if (match) {
>                 chip_type = (uintptr_t)match;
>                 name = client->name;
>         } else if (id) {
>                 chip_type = (enum inv_devices)
>                         id->driver_data;
>                 name = id->name;
>         } else {
>                 return -ENOSYS;
>         }

I don't consider that part of the ABI, as e.g. converting from board files
to DT would change the name.
In addition, using id->name breaks multiple instances of the same device.

I applaud more unification ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds