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From: Jesse Barnes <jbarnes@virtuousgeek.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [Bug #12608] 2.6.29-rc powerpc G5 Xorg legacy_mem regression
Date: Sat, 7 Feb 2009 15:15:20 -0800
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On Friday, February 6, 2009 7:05 pm Benjamin Herrenschmidt wrote:
> On Fri, 2009-02-06 at 14:45 -0800, Jesse Barnes wrote:
> > +    if (Base <= 1024*1024) {
> > +        /* Try legacy_mem (may not be available or implemented) */
> > +        if ((fd = linuxOpenLegacy(dev, "legacy_mem")) < 0) {
> > +            addr = mmap(NULL, Size, PROT_READ|PROT_WRITE, MAP_SHARED,
> > fd, Base); +            close(fd);
> > +            if (addr && addr != MAP_FAILED)
> > +                return addr;
> > +        }
> >      }
> > -    return addr;
> > +
> > +    /* Fall back to old method if legacy_mem fails or Base >= 1M */
> > +    return linuxMapPci(ScreenNum, Flags, dev, Base, Size,
> > PCIIOC_MMAP_IS_MEM); }
>
> I don't like the fallback if legacy_mem exists and returns an error,
> that's an indication that legacy memory is -not- available and thus
> whatever 'fallback' X will try (supposedly using /dev/mem) will be
> horribly broken and will probably end up scribbling all over system
> memory :-)

Yeah, but unless we fix all the callers (and possibly their callers), not 
falling back will keep X from starting...

-- 
Jesse Barnes, Intel Open Source Technology Center