AMD IOMMU Driver Reworked For Linux 5.5

With the IOMMU updates for the Linux 5.5 kernel there is a major rework to the AMD IOMMU driver to make use of more common DMA IOMMU code for implementing the DMA API but with an admitted risk of potential new regressions.

The AMD IOMMU Linux driver now makes use of the "dma-iommu" kernel code that allows the driver to be lightened up by several hundred lines of code thanks to the code sharing/re-use. Besides the DMA IOMMU changes, the AMD IOMMU driver now also has multiple PCI DMA alias support.

The IOMMU updates acknowledge, "This gets rid of quite some code in the driver itself, but also has some potential for regressions (non are known at the moment)."

The IOMMU changes for Linux 5.5 also include Qualcomm SMMUv2 support with the SDM845 SoC, ARM SMMU driver changes, Renesas IOMMU driver changes working towards future hardware support, and other changes.