Re: [ACPI] Re: Linux 2.4.26-rc1 (cmpxchg vs 80386 build)

From: Willy Tarreau
Date: Tue Mar 30 2004 - 09:27:29 EST

On Tue, Mar 30, 2004 at 08:15:46AM -0500, Richard B. Johnson wrote:
> On Tue, 30 Mar 2004, Alan Cox wrote:
> > On Llu, 2004-03-29 at 23:07, Len Brown wrote:
> > > Linux uses this locking mechanism to coordinate shared access
> > > to hardware registers with embedded controllers,
> > > which is true also on uniprocessors too.
> >
> > If the ACPI layer simply refuses to run on a CPU without cmpxchg
> > then I can't see there being a problem, there don't appear to be
> > any 386 processors with ACPI
> >
> Yep, but to get to use cmpxchg, you need to compile as a '486 or
> higher. This breaks i386.

OK, so why not compile the cmpxchg instruction even on i386 targets
to let generic kernels stay compatible with everything, but disable
ACPI at boot if the processor does not feature cmpxchg ? This could
be helpful for boot/install kernels which try to support a wide
range of platforms, and may need ACPI to correctly enable interrupts
on others.


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