Re: [patch -mm] Make check_signature() depend on CONFIG_HAS_IOMEM

Andrew Morton
2007-06-28T23:02:23Z

On Thu, 28 Jun 2007 18:45:11 -0400
Jeff Dike <jdike@addtoit.com> wrote:

> On Thu, Jun 28, 2007 at 11:25:37PM +0100, Alan Cox wrote:
> > This completely bogus. readb() should be present on M68K, fix the
> > platform to implement readb() for MMIO, even if your MMIO readb is a
> > moveb instruction.
> >
> > check_signature is relevant for anything with MMIO space (for example you
> > can legitimately want to check_signature a MAC68K Nubus ROM).
> >
> > S/390 is a bit of a special case as no S/390 usage of check_signature
> > appears sane but equally it isn't used so you can stub it out.
>
> This is a problem for UML too.
>
> I have a patch in my tree, which basically stubs readb, waiting to see
> how this is fixed for the other arches.
>

What a mess.

I guess we could add an empty readb() implementation to lib/lib.a so the
arch will pick that up if all else fails. But it's pretty stinky. And
it won't work either because we don't know at compile-time to declare
the prototype for that thing appropriately.

So... what's the proper fix here? "The arch must implement readb"? That's
bad: if the arch really cannot implement readb(), we want builds to fail
if someone tries to use it.

I think I'll go shopping instead.