From: Olof Johansson <olof@lixom•net>
To: Benjamin Herrenschmidt <benh@kernel•crashing.org>
Cc: linuxppc-dev@ozlabs•org,
"cbe-oss-dev@ozlabs•org" <cbe-oss-dev@ozlabs•org>,
Arnd Bergmann <arnd@arndb•de>
Subject: Re: [Cbe-oss-dev] [PATCH 3/3] Cell IOMMU static mapping support
Date: Mon, 28 Jan 2008 15:48:13 -0600 [thread overview]
Message-ID: <20080128214813.GA24416@lixom.net> (raw)
In-Reply-To: <1201554977.6815.189.camel@pasglop>
On Tue, Jan 29, 2008 at 08:16:17AM +1100, Benjamin Herrenschmidt wrote:
>
> On Mon, 2008-01-28 at 10:23 -0600, Olof Johansson wrote:
> > Ok, makes sense.
> >
> > I was going to protest the hack for >32GB configs, with the motivation
> > that just using the htab-backed window is way too small for such a
> > config. However, with 32GB memory and 4K pages, that window is 512MB, so
> > we should be fine.
>
> Might be a problem with 64K pages tho... Or do we use the same
> calculation ?
The current code is hardcoded at page shift 12. That's probably the
safest thing to do, since even though PAGE_SHIFT might be 16, if we're
doing the software-based 64K approach we can't use a smaller table.
See htab_get_table_size() in arch/powerpc/mm/hash_utils_64.c.
> In addition, on those blades, really the only device that is limited to
> 32 bits (and thus is forced to use the iommu remapped region) is USB.
>
> > Having that described in the patch (or at least in the patch description)
> > to make it more clear could be good. That, and the fact that the mapping
> > is offset on <32GB memory machines, and thus not really a 1:1 mapping.
>
> Should be called a "linear" mapping.
Yep. Linear with a fixed offset.
> > Does the cell I/O bridge reflect out accesses to 2-4GB on the bus
> > again? If not, that could be another place to stick the dynamic range
> > for large config machines.
>
> On the PCI bus itself, 2-4GB is where MMIO sits.
Depending on the implementation, 2-4GB accesses _from_ PCI could mean
something else. But for most machines it doesn't, and I'm guessing cell
is one of those.
-Olof
next prev parent reply other threads:[~2008-01-28 21:48 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-01-25 10:45 [PATCH 1/3] Add set_dma_ops() to match get_dma_ops() Michael Ellerman
2008-01-25 10:45 ` [PATCH 2/3] Allocate the hash table under 1G on cell Michael Ellerman
2008-02-05 0:23 ` Benjamin Herrenschmidt
2008-01-25 10:45 ` [PATCH 3/3] Cell IOMMU static mapping support Michael Ellerman
2008-01-25 13:12 ` [Cbe-oss-dev] " Geert Uytterhoeven
2008-01-26 2:51 ` Olof Johansson
2008-01-28 11:41 ` [Cbe-oss-dev] " Arnd Bergmann
2008-01-28 16:23 ` Olof Johansson
2008-01-28 21:16 ` Benjamin Herrenschmidt
2008-01-28 21:48 ` Olof Johansson [this message]
2008-01-28 21:37 ` Benjamin Herrenschmidt
2008-01-28 21:18 ` Benjamin Herrenschmidt
2008-02-05 0:23 ` [PATCH 1/3] Add set_dma_ops() to match get_dma_ops() Benjamin Herrenschmidt
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