On Mon, Jun 06, 2011 at 12:36:13PM -0400, Ohad Ben-Cohen wrote: > On Mon, Jun 6, 2011 at 6:35 PM, Roedel, Joerg <Joerg.Roedel@xxxxxxx> wrote: > > On Mon, Jun 06, 2011 at 11:15:30AM -0400, Ohad Ben-Cohen wrote: > > > >> This is insufficient; users need somehow to tell what page sizes are > >> supported by the underlying hardware (we can't assume host page-sizes, > >> and we want to use bigger pages whenever possible, to relax the TLB > >> pressure). > > / > > What does the IOMMU-API user need this info for? On the x86 IOMMUs these > > details are handled transparently by the IOMMU driver. > > That's one way to do that, but then it means duplicating this logic > inside the different IOMMU implementations. > > Take the OMAP (and seemingly MSM too) example: we have 4KB, 64KB, 1MB > and 16MB page-table entries. When we map a memory region, we need to > break it up to a minimum number of pages (while validating > sizes/alignments are sane). It's not complicated, but it can be nice > if it'd be implemented only once. Well, it certainly makes sense to have a single implementation for this. But I want to hide this complexity to the user of the IOMMU-API. The best choice is to put this into the layer between the IOMMU-API and the backend implementation. > In addition, unless we require 'va' and 'pa' to have the exact same > alignment, we might run into specific page configuration that the > IOMMU implementation cannot restore on ->unmap, since unmap only takes > 'va' and 'order'. So we will either have to supply 'pa' too, or have > the implementation remember the mapping in order to unmap it later. > That begins to be a bit messy... That interface is not put into stone. There were other complains about the ->unmap part recently, so there is certainly room for improvement there. Regards, Joerg -- AMD Operating System Research Center Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach General Managers: Alberto Bozzo, Andrew Bowd Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
