On Wed, Dec 13, 2006 at 09:34:16PM +0100, Karsten Weiss wrote: > FWIW: As far as I understand the linux kernel code (I am no kernel > developer so please correct me if I am wrong) the PCI dma mapping code is > abstracted by struct dma_mapping_ops. I.e. there are currently four > possible implementations for x86_64 (see > linux-2.6/arch/x86_64/kernel/) > > 1. pci-nommu.c : no IOMMU at all (e.g. because you have < 4 GB memory) > Kernel boot message: "PCI-DMA: Disabling IOMMU." > > 2. pci-gart.c : (AMD) Hardware-IOMMU. > Kernel boot message: "PCI-DMA: using GART IOMMU" (this message > first appeared in 2.6.16) > > 3. pci-swiotlb.c : Software-IOMMU (used e.g. if there is no hw iommu) > Kernel boot message: "PCI-DMA: Using software bounce buffering > for IO (SWIOTLB)"
Used if there's no HW IOMMU *and* it's needed (because you have >4GB memory) or you told the kernel to use it (iommu=soft). > 4. pci-calgary.c : Calgary HW-IOMMU from IBM; used in pSeries servers. > This HW-IOMMU supports dma address mapping with memory proctection, > etc. > Kernel boot message: "PCI-DMA: Using Calgary IOMMU" (since > 2.6.18!) Calgary is found in pSeries servers, but also in high-end xSeries (Intel based) servers. It would be a little awkward if pSeries servers (which are based on PowerPC processors) used code under arch/x86-64 :-) > BTW: It would be really great if this area of the kernel would get some > more and better documentation. The information at > linux-2.6/Documentation/x86_64/boot_options.txt is very terse. I had to > read the code to get a *rough* idea what all the "iommu=" options > actually do and how they interact. Patches happily accepted :-) Cheers, Muli - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/