VMbus synthetic devices are not represented in the ACPI DSDT -- only
the top level VMbus device is represented. As a result, on ARM64
coherence information in the _CCA method is not specified for
synthetic devices, so they default to not hardware coherent.
Drivers for some of these synthetic devices have been recently
updated to use the standard DMA APIs, and they are incurring extra
overhead of unneeded software coherence management.

Fix this by propagating coherence information from the VMbus node
in ACPI to the individual synthetic devices. There's no effect on
x86/x64 where devices are always hardware coherent.
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/1648138492-2191-2-git-send-email-mikelley@microsoft.comSigned-off-by: Wei Liu <wei.liu@kernel.org>