commit fff5d99225107f5f13fe4a9805adc2a1c4b5fb00
author Geert Uytterhoeven <geert+renesas@glider.be> Fri Dec 16 14:28:42 2016 +0100
committer Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mon Dec 19 09:05:20 2016 -0500
tree 0b9748236ea4580bc44f9a24ec27c215cb46ed9b
parent ae7871be189cb41184f1e05742b4a99e2c59774d

swiotlb: Add swiotlb=noforce debug option

On architectures like arm64, swiotlb is tied intimately to the core
architecture DMA support. In addition, ZONE_DMA cannot be disabled.

To aid debugging and catch devices not supporting DMA to memory outside
the 32-bit address space, add a kernel command line option
"swiotlb=noforce", which disables the use of bounce buffers.
If specified, trying to map memory that cannot be used with DMA will
fail, and a rate-limited warning will be printed.

Note that io_tlb_nslabs is set to 1, which is the minimal supported
value.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>