From mboxrd@z Thu Jan  1 00:00:00 1970
From: Benjamin Herrenschmidt <benh-XVmvHMARGAS8U2dJNN8I7kB+6BGkLq7r@public.gmane.org>
Subject: Re: [Bug #12608] 2.6.29-rc powerpc G5 Xorg legacy_mem regression
Date: Sat, 07 Feb 2009 14:05:10 +1100
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To: Jesse Barnes <jbarnes-Y1mF5jBUw70BENJcbMCuUQ@public.gmane.org>
Cc: Hugh Dickins <hugh-DTz5qymZ9yRBDgjK7y7TUQ@public.gmane.org>, "Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org>, Linux Kernel Mailing List <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Kernel Testers List <kernel-testers-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>

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 :-)

Ben.