From: Ralf Baechle <ralf@linux-mips.org>
To: "Maciej W. Rozycki" <macro@linux-mips.org>
Cc: Paul Chapman <paul.chapman@BrockU.CA>, linux-mips@linux-mips.org
Subject: Re: ip27 PCI devices
Date: Tue, 12 Apr 2005 12:42:52 +0100 [thread overview]
Message-ID: <20050412114252.GE5573@linux-mips.org> (raw)
In-Reply-To: <Pine.LNX.4.61L.0504121213400.18606@blysk.ds.pg.gda.pl>
On Tue, Apr 12, 2005 at 12:18:15PM +0100, Maciej W. Rozycki wrote:
> > > I've been experimenting with trying various PCI cards I have lying
> > > around in my Origin 200, to see if I can make any of them work.
> >
> > The current Linux implementation limits IP27 to cards with 64-bit
> > addressing capability.
>
> Do we have a problem with our implementation of PCI DMA masks or is the
> low 4GB of PCI address space already consumed on this system? The problem
> is most 32-bit PCI cards unfortunately do not support DAC.
32-bit devices can only address a tiny fraction of the address space on
IP27. To make matters more interesting, there is no memory at all in the
low 4GB of the crosstalk address space, so 32-bit PCI has to rely on the
yet non-existing support for the IOMMU. SGI trying to save a little too
much money on the external SRAM for the IOMMU in the Origin 200 finally
made it a hard to use in an OS, deadlock prone thing.
Ralf
prev parent reply other threads:[~2005-04-12 11:43 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-04-11 20:30 ip27 PCI devices Paul Chapman
2005-04-12 10:58 ` Ralf Baechle
2005-04-12 11:18 ` Maciej W. Rozycki
2005-04-12 11:42 ` Ralf Baechle [this message]
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