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

[Julien Grall <julien@xxxxxxx>]

Hi,

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
> support.
>
> 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.
Cheers,

--
Julien Grall