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Re: [PATCH] xen/arm: Remove EXPERT dependancy


On 22/10/2020 02:43, Elliott Mitchell wrote:
Linux requires UEFI support to be enabled on ARM64 devices.  While many
ARM64 devices lack ACPI, the writing seems to be on the wall of UEFI/ACPI
potentially taking over.  Some common devices may need ACPI table

Presently I think it is worth removing the dependancy on CONFIG_EXPERT.

The idea behind EXPERT is to gate any feature that is not considered to be stable/complete enough to be used in production.

I don't consider the ACPI complete because the parsing of the IORT (used to discover SMMU and GICv3 ITS) is not there yet.

I vaguely remember some issues on system using SMMU (e.g. Thunder-X) because Dom0 will try to use the IOMMU and this would break PV drivers.

Therefore I think we at least want to consider to hide SMMUs from dom0 before removing EXPERT. Ideally, I would also like the feature to be tested in Osstest.

The good news is Xen Project already has systems (e.g. Thunder-X, Softiron) that can supported ACPI. So it should hopefully be a matter to tell them to boot with ACPI rather than DT.


Julien Grall



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