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

On Thu, Oct 22, 2020 at 02:17:13PM -0700, Stefano Stabellini wrote:
> On Thu, 22 Oct 2020, Julien Grall wrote:
> > 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.
> Yes, and from that point of view I don't think we want to remove EXPERT
> from ACPI yet. However, the idea of hiding things behind EXPERT works
> very well for new esoteric features, something like memory introspection
> or memory overcommit. It does not work well for things that are actually
> required to boot on the platform.
> Typically ACPI systems don't come with device tree at all (RPi4 being an
> exception), so users don't really have much of a choice in the matter.
> >From that point of view, it would be better to remove EXPERT from ACPI,
> maybe even build ACPI by default, *but* to add a warning at boot saying
> something like:
> "ACPI support is experimental. Boot using Device Tree if you can."
> That would better convey the risks of using ACPI, while at the same time
> making it a bit easier for users to boot on their ACPI-only platforms.

This matches my view.  I was thinking about including "default y", but I
felt the chances of that getting through were lower.  I concur with a
warning on boot being a good approach.

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