On 2018-01-24 10:43 AM, Christian König wrote: > Am 24.01.2018 um 10:17 schrieb Chunming Zhou: >> dma path is low than ttm pool. > > That won't work correctly in some cases. > >> Question: >> But why need two path? What spicific problem can be solved by dma path? > > That is mostly for ARM and some (rare) x86 platforms without IOMMU where > some memory is above the 40bit limit in the PCIe address space. > > Our GPUs can unfortunately only deal with 40bits of address space, so on > those systems we need to go the slow path and make sure that we don't > try to touch that high memory. > > What we could really improve is the detection using swiotlb_nr_tbl(), > cause that is actually completely wrong. FWIW, there are other cases where SWIOTLB is needed, e.g. Secure Memory Encryption: https://bugs.freedesktop.org/show_bug.cgi?id=104437 -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer
