net: hns3: default enable tx bounce buffer when smmu enabled

net: hns3: default enable tx bounce buffer when smmu enabled

The SMMU engine on HIP09 chip has a hardware issue.
SMMU pagetable prefetch features may prefetch and use a invalid PTE
even the PTE is valid at that time. This will cause the device trigger
fake pagefaults. The solution is to avoid prefetching by adding a
SYNC command when smmu mapping a iova. But the performance of nic has a
sharp drop. Then we do this workaround, always enable tx bounce buffer,
avoid mapping/unmapping on TX path.

This issue only affects HNS3, so we always enable
tx bounce buffer when smmu enabled to improve performance.

Fixes: 295ba232a8c3 ("net: hns3: add device version to replace pci revision")
Signed-off-by: Peiyang Wang <[email protected]>
Signed-off-by: Jian Shen <[email protected]>
Signed-off-by: Jijie Shao <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>