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

From: Jonathan Cameron <jic23@kernel.org>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Biju Das <biju.das.jz@bp.renesas.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>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	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, 7 Aug 2023 20:45:05 +0100	[thread overview]
Message-ID: <20230807204505.5f3f245e@jic23-huawei> (raw)
In-Reply-To: <ZNEFjyAloqlkMWn7@smile.fi.intel.com>

On Mon, 7 Aug 2023 17:54:07 +0300
Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

> On Sun, Aug 06, 2023 at 02:29:50PM +0100, Jonathan Cameron wrote:
> > On Sat, 5 Aug 2023 17:42:21 +0000
> > Biju Das <biju.das.jz@bp.renesas.com> wrote:  
> > > > On Fri,  4 Aug 2023 17:17:24 +0100
> > > > Biju Das <biju.das.jz@bp.renesas.com> wrote:  
> 
> ...
> 
> > > + * Besides the fact that some drivers abuse the device ID driver_data type
> > > + * and claim it to be integer, for the bus specific ID tables the driver_data
> > > + * may be defined as kernel_ulong_t. For these tables 0 is a valid response,
> > > + * but not for this function. It's recommended to convert those either to avoid
> > > + * 0 or use a real pointer to the predefined driver data.  
> 
> > We still need to maintain consistency across the two tables, which
> > is a stronger requirement than avoiding 0.  
> 
> True. Any suggestion how to amend the above comment? Because the documentation
> makes sense on its own (may be split from the series?).

For bus ID tables it is fine right now as long as no one checks for NULL.
I guess adding this to the i2c_get_match_data and spi equivalent wrapper
functions might avoid someone shooting themselves in the foot (I've done it
for starters more than once).

> 
> > Some drivers already do that by forcing the enum used to start at 1 which
> > doesn't solver the different data types issue.  
> 
> And some maintainers do not want to see non-enum values in i2c ID table.
> *Shrug*.
> 

That leaves us stuck unless we move to a form where the i2c ID table isn't
used if there is an of_device_id table (or maybe we invent yet another table
and if that is present it is used for dt and were i2c_device_id is used and
hence becomes an opt in?  That will also be tricky however.

Jonathan