Re: mmap question on ppc440

[Josh Boyer <jwboyer@linux.vnet.ibm.com>]

On Wed, 07 Nov 2007 09:02:10 +1100
Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> 
> On Tue, 2007-11-06 at 07:50 +0100, Stefan Roese wrote:
> > On Monday 05 November 2007, Josh Boyer wrote:
> > > > I am attempting to access the CPLD on the AMCC Sequoia board from
> > > > user-land.  I open /dev/mem, and mmap it, then try to access the
> > > > resulting pointer.  That works fine when accessing physical addresses
> > > > that correspond to RAM, but as soon as I try to access the CPLD at
> > > > physical address 0xc0000000, I get an infinite machine check.
> > >
> > > That's because the CPLD is actually at physical address 0x1C0000000.
> > > Yay for 36-bit physical addresses.
> > 
> > Right. Are you using arch/ppc or arch/powerpc? If it's arch/ppc you could
> > give the following patch a try:
> > 
> > @@ -275,6 +275,14 @@
> >  {
> >         size_t size = vma->vm_end - vma->vm_start;
> > 
> > +#if defined(CONFIG_44x) && !defined(CONFIG_PPC_MERGE)
> > +       /*
> > +        * 2006-08-07: sr
> > +        * Needed on 44x-er systems for 36bit addresses (like pci on 440gx)
> > +        */
> > +       vma->vm_pgoff = (fixup_bigphys_addr(vma->vm_pgoff << PAGE_SHIFT, size) >> PAGE_SHIFT);
> > +#endif
> > +
> >         if (!valid_mmap_phys_addr_range(vma->vm_pgoff, size))
> >                 return -EINVAL;
> 
> I think we need to ditch the bigphys fixup stuff and come up with a way
> to make /dev/mem work with the actual 36 bits offsets (after all, it's
> all pgoff, it should work).

We did ditch bigphys in arch/powerpc.  mmap64 works apparently.

> The other problem is X of course... 32 bits X server currently cannot
> cope with physical addresses > 32 bits at all. They will just blow up or
> randomly scribble over /dev/mem.
> 
> The solution is libpciaccess and the new pci-rework branch of X which
> uses it, but I haven't had a chance to test that properly yet on 4xx.

Um... because arch/powerpc 4xx doesn't have PCI support? :)  You and
Valentine and Vitaly keep trading emails about it though, which is a
good sign.

josh