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

Jonathan Cameron
2023-08-08T19:50:49Z

On Mon, 7 Aug 2023 13:37:12 -0700
Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:

> On Mon, Aug 07, 2023 at 05:54:07PM +0300, Andy Shevchenko 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?).
> >
> > > 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*.
>
> So in legacy ID lookup path we can safely assume that values below 4096
> are scalars and return NULL from the new device_get_match_data(). This
> way current drivers using the values as indices or doing direct
> comparisons against them can continue doing manual look up and using
> them as they see fit. And we can convert the drivers at our leisure.

Good idea. Though I suspect there may still be nasty cases. People have
been known to put chip ID values in these fields so that they can then
match them against a who am I register as a 'detect it's the right part' check.

No idea if we have any drivers doing that but if there are hopefully not too many!

Jonathan

>
> Thanks.
>