RE: [PATCH] powerpc/usb: use unsigned long to type cast an address of ioremap

["David Laight" <David.Laight@ACULAB.COM>]

> >> >  usb_sys_regs =3D (void *)dr_regs + USB_DR_SYS_OFFSET;
>=20
> > But that is invalid C.
>=20
> What's invalid about it?  I haven't tried compiling this=20
> specific line of code, but I've done stuff like it in the past many
times.
>=20
> Are you talking about adding an integer to a void pointer? =20
> If so, then that's something that gcc supports and that the kernel
uses=20
> all over the place.

Arithmetic on 'void *' should not be done. I know some versions of
gcc allow it (provided some warning level/option is enabled) but
that doesn't mean it is valid.
My suspicions are that is was allowed due to the way 'void *'
was originally bodged into gcc.

> A char* is incorrect because a char could be more=20
> than one byte, in theory.

It is somewhat difficult to untangle the standard, but
sizeof (char) is defined to be one.

Of course, the C language doesn't actually require that
you can converts between pointers to different types in
any well-defined manner. But most of the low level device
access assumes an adequately linear address space.

	David