linux-kernel - Re: [Bug #12608] 2.6.29-rc powerpc G5 Xorg legacy

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Date:	Sat, 07 Feb 2009 14:05:10 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Hugh Dickins <hugh@...itas.com>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>
Subject: Re: [Bug #12608] 2.6.29-rc powerpc G5 Xorg legacy_mem regression

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.


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