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.
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