On Thu, 11 Dec 2008, Kumar Gala wrote: > On Dec 11, 2008, at 10:07 PM, Trent Piepho wrote: >> On Thu, 11 Dec 2008, Kumar Gala wrote: >> > On Dec 11, 2008, at 6:04 AM, maillist.kernel wrote: >> > > In the system, the total PCI address needed is about 3GB, so I want to >> > > know >> > > how to support it in linux. mpc8548 has 36-bit real address, and can >> > > support 32GB PCIE address space, but in linux, there is only 1GB kernel >> > > space, how to map the 3GB pci address to kernel? Is the 36-bit real >> > > address only used to support large memory(>4GB) for muti-threads? >> > >> > The 36-bit support is current (in tree) in complete. Work is in progress >> > to >> > add swiotlb support to PPC which will generically enable what you want to >> > accomplish. >> >> Don't the ATMU windows in the pcie controller serve as a IOMMU, making >> swiotlb >> unnecessary and wasteful? > > Nope. You have no way to tell when to switch a window as you have no idea > when a device might DMA data.
Isn't that what dma_alloc_coherent() and dma_map_single() are for? It sounded like the original poster was talking about having 3GB of PCI BARs. How does swiotlb even enter the picture for that? >From what I've read about swiotlb, it is a hack that allows one to do DMA with 32-bit PCI devices on 64-bit systems that lack an IOMMU. It reserves a large block of RAM under 32-bits (technically it uses GFP_DMA) and doles this out to drivers that allocate DMA memory. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
