Details
-
Type:
Bug
-
Status: Resolved
-
Priority:
Minor
-
Resolution: Won't Fix
-
Affects Version/s: V2.0.0.0, V2.0.1.0, V2.1.0.0, V2.1.1.0
-
Fix Version/s: None
-
Component/s: Linux Driver
-
Labels:None
-
Account:SDO Driver (SDODRIVER)
Description
On x86 (AMD64) platform when using DMA, depending on the kernel version, the warning "x86/PAT: map pfn RAM range req uncached-minus for [mem 0xxxxx-0xxxxx], got write-back" may occur.
The kernels assumption DMA memory is uncached by default may be wrong on DMA coherent platform/devices. The fix in the kernel of the page mapping properties reveals this as warning now.
The libcifx accesses the DMA buffer in user space via mmap. The mapping is done via the generic UIO kernel module which expects uncached memory but lacks the check and fixup.
On DMA coherent platforms the warning may be ignored as it may improve the performance. In case of doubts the memory can be explicitly set to uncached via the appended patch "set_dma_mem_to_uc.patch".
FAQ linux driver: https://kb.hilscher.com/x/iMUJCQ