Re: [PATCH 2/4] usb: typec: tcpci_rt1711h: Convert enum->pointer for data in the match tables

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Tue, Aug 22, 2023 at 09:21:19AM +0200, Geert Uytterhoeven wrote:
> On Mon, Aug 21, 2023 at 7:09 PM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> 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@linux.intel.com> 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@linux.intel.com> 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().

Yes, that parameter is void * due to calling kfree(free_irq(...)).
So, that's argument for my concerns.

> > 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.

Nope, it uses the very same mod_devicetable.h in both.

> Still, changing the type would be a lot of work,
> for IMHO no real gain.

So, stale mate here, then?

> > 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.

At least something we have agreed on :-)

-- 
With Best Regards,
Andy Shevchenko