From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [Cbe-oss-dev] [PATCH 3/3] Cell IOMMU static mapping support From: Benjamin Herrenschmidt To: Olof Johansson In-Reply-To: <20080128162343.GA19859@lixom.net> References: <9ce4678eef9e50908969eb1ef8470e307f3076ff.1201257905.git.michael@ellerman.id.au> <20080126025117.GA28066@lixom.net> <200801281241.49059.arnd@arndb.de> <20080128162343.GA19859@lixom.net> Content-Type: text/plain Date: Tue, 29 Jan 2008 08:16:17 +1100 Message-Id: <1201554977.6815.189.camel@pasglop> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org, "cbe-oss-dev@ozlabs.org" , Arnd Bergmann Reply-To: benh@kernel.crashing.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 ? 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. > 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. Ben.