generic memory addresses

[Greg KH]

On Thu, Apr 06, 2017 at 08:11:34PM +1000, Tobin C. Harding wrote:
> On Thu, Apr 06, 2017 at 08:08:20AM +0200, Greg KH wrote:
> > On Thu, Apr 06, 2017 at 10:31:01AM +1000, Tobin C. Harding wrote:
> > > Why is there code in-tree that declares generic memory addresses as
> > > unsigned int?
> > > 
> > > Linux Device Drivers 3rd Edition page 289
> > >  Therefore, generic memory addresses in the kernel are usually unsigned
> > >  long, exploiting the fact that pointers and long integers are always
> > >  the same size, at least on all the platforms currently supported by
> > >  Linux.
> > > 
> > > It would therefore seem like a bug to declare a generic memory address
> > > as an unsigned int in code that can run on 64 bit machines.
> > 
> > I agree, that does seem like a bug.
> 
> The example that started me looking at this is in
> drivers/mmc/core/sdio_io.c
> 
> int sdio_memcpy_fromio(struct sdio_func *func, void *dst,
> 	unsigned int addr, int count)
> {
> 	return sdio_io_rw_ext_helper(func, 0, addr, 1, dst, count);
> }
> 
> Is there perhaps some reason that it can be guaranteed that this
> address is for 32 bit architecture. Is it acceptable to think that mmc
> cards are never more than 32 bit and this code will never have its use
> extended to where 64 bit addresses are used?

How do you know this is a "real" address, and not just an sdio
"address"?  The two are very different.  See the SDIO spec for details
about how that protocol works if you are curious.

So here, this isn't an issue, and yes, sdio drivers do work just fine on
64bit systems, lots of us use these drivers all the time on both laptops
and embedded systems running a 64bit kernel.

hope this helps,

greg k-h