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List:       dri-devel
Subject:    Re: "no scatter/gather memory" ?
From:       Jesse Barnes <jbarnes () sgi ! com>
Date:       2005-03-05 17:42:23
Message-ID: 200503050942.23605.jbarnes () sgi ! com
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On Friday, March 04, 2005 6:01 pm, Roland Scheidegger wrote:
> Paul Mackerras wrote:
> > Note that that check is also wrong for ppc64.  I think it is going to
> > be wrong for most 64-bit platforms, since it is assuming that you can
> > never have ram at a higher physical address than any I/O devices.  On
> > 64-bit platforms it is quite common to have some ram and some I/O
> > below 4GB, and some more ram above 4GB.
> >
> > I don't see why we need the check anyway, unless some architecture
> > (x86?) will actually panic if you try to ioremap a physical address
> > that is below virt_to_phys(high_memory) or something.
>
> Wouldn't this check even break on x86 with PAE? Those boxes certainly
> have parts of their ram mapped above io memory too. Or does that
> high_memory variable stay below 4GB with PAE?

I think the start of high memory will stay below 4G, but the check should 
probably be removed anyway.  If we really want to make sure that a given 
offset is in I/O space, we should check that explicitly, and not rely on some 
'top of real memory' type variable, since that's inherently non-portable.

Jesse


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