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