Hi Andy,
CC DT
On Mon, Aug 21, 2023 at 7:09 PM Andy Shevchenko
<andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> On Mon, Aug 21, 2023 at 05:40:05PM +0200, Geert Uytterhoeven wrote:
> > On Mon, Aug 21, 2023 at 5:25 PM Andy Shevchenko
> > <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> > > On Mon, Aug 21, 2023 at 03:27:43PM +0200, Geert Uytterhoeven wrote:
> > > > On Mon, Aug 21, 2023 at 3:04 PM Andy Shevchenko
> > > > <andriy.shevchenko@xxxxxxxxxxxxxxx> wrote:
> > > > > On Sun, Aug 20, 2023 at 07:44:00PM +0100, Biju Das wrote:
>
> ...
>
> > > > > For all your work likes this as I noted in the reply to Guenter that
> > > > > the couple of the selling points here are:
> > > > > 1) avoidance of the pointer abuse in OF table
> > > > > (we need that to be a valid pointer);
> > > >
> > > > There is no pointer abuse: both const void * (in e.g. of_device_id)
> > > > and kernel_ulong_t (in e.g. i2c_device_id) can be used by drivers
> > > > to store a magic cookie, being either a pointer, or an integer value.
> > > > The same is true for the various unsigned long and void * "driver_data"
> > > > fields in subsystem-specific driver structures.
> > >
> > > (void *)5 is the abuse of the pointer.
> > > We carry something which is not a valid pointer from kernel perspective.
> >
> > But the data field is not required to be a valid pointer.
> > What kind and type of information it represents is specific to the driver.
>
> Where to find necessary information which is not always an integer constant.
> For example, for the driver data that has callbacks it can't be invalid pointer.
If the driver uses it to store callbacks, of course it needs to be a
valid pointer. But that is internal to the driver. It is not that
we're passing random integer values to a function that expects a
pointer that can actually be dereferenced.
> Since OF ID table structure is universal, it uses pointers. Maybe you need to
> update it to use plain integer instead?
It is fairly common in the kernel to use void * to indicate a
driver-specific cookie, being either a real pointer or an integral
value, that is passed verbatim. See also e.g. the "dev" parameter
of request_irq().
> I think there is no more sense to continue this. We have to admit we have
> a good disagreement on this and I do not see any way I can agree with your
> arguments. Note, I'm fine if you "fix" OF ID structure to use kernel_ulong_t.
of_device_id is also used in userspace (e.g. modutils), but I believe
that uses a copy of the structure definition, not the definition from
the kernel headers. Still, changing the type would be a lot of work,
for IMHO no real gain.
> The only objection there is that it may not carry on the const qualifier,
> which I personally find being a huge downside of the whole driver_data.
> I believe you haven't objected that.
Having const is nice, indeed.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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
