Hi!
I try to port our 3D scanner driver to kernel v4.9 and I have a trouble.
I can not find a correct way to allocate DMA memory with correct iommu
setup. Could you help me?
HW: Tegra X1 and Tegra X2 (arm64), our PCIe bus master device uses about
200M of system memory to send data from sensors. The memory is organized
in circular buffer (8 frames) and one info page (only 8 bytes are used now).
Old driver works at kernel v3.10 and some memory access rules are new in
v4.9, such as iommu.
I try to use reserved memory region attached to the device in device
tree and dma_alloc_coherent() to allocate the buffer. (Then I am going
to find correct flags to turn off coherency and to sync data to CPU
manually when full frame is arrived.)
Unfortunately, iommu does not set the area.
I've tried to find why. I see iommu calls in general dma memory
allocation where arch-dependent dma_ops are used (and it sets iommu
area, I can see it in /sys/kernel/debug), but I can not find the calls
in per-device allocation track. So I do not see if my code is not
working because of my bugs or I use wrong concept or it is bug in kernel.
Is there iommu setup in per-device reserved memory allocator (or may be
earlier in memory reservation)? If no, why? Is it a feature or a bug?
While there are some significant changes in the code from v4.9 to v5.8,
I have not found any related to iommu in the area, so I think it may be
the same problem with latest kernel version.
Thanks,
Sergei Pyptev
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