Am 24.01.2018 um 10:49 schrieb Michel Dänzer: > 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 Oh! Good point, didn't noticed that bug before. But yes the rational makes perfect sense. Regards, Christian.
