Re: [PATCH v2 4/6] ACPI: ARM: exclude DMI calls

[Matthew Garrett <mjg59@srcf.ucam.org>]

On Tue, Dec 03, 2013 at 06:30:48PM -0700, Al Stone wrote:

> I thought I could get this to work, but I am going to have to defer
> to the ACPICA upstream folks.  For the time being, I think that all
> of the architectures that want to use ACPI in either legacy mode or
> in stripped down reduced HW mode will have to use different kernels,
> one for each mode.  I thought there might be enough safety checks to
> allow the kernel to boot in legacy mode and switch into reduced HW at
> boot, but there are not, in my opinion.  I don't see a way to make the
> switch *and* maintain conformance with the spec without significant
> change to ACPICA itself.

Ugh. That needs fixing. There's been a huge amount of work done to 
ensure that x86 only needs a single kernel image for 64-bit, it really 
needs to be runtime. We shouldn't have merged it in this state.

> For example, enforcing that various functions are not allowed while
> in reduced HW mode could be done by a check of the reduced HW flag on
> entry.  If it is set, return the value the function would have returned
> had it been stubbed out for reduced HW mode.  This is simple enough but
> to do so would require modifying at least 29 functions in ACPICA, by my
> count, not something upstream is particularly keen on -- nor am I.  I'd
> rather step back and work with ACPICA over the longer term and see if
> there's some way to get this functionality implemented properly instead
> of trying to bolt it on somehow.

How many of those are calls that we'll actually execute in the HW 
reduced case?

-- 
Matthew Garrett | mjg59@srcf.ucam.org