Re: [PATCH/RFC] ACPICA: disable ACPI 2.0 _GTS/_BFS support

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Friday, 19 of December 2008, Len Brown wrote:
> From: Len Brown <len.brown@intel.com>
> Organization: Intel Open Source Technology Center
> 
> ACPI 2.0 defined two new methods in the suspend/resume sequence,
> _GTS (Going to Sleep) and _BFS (Back from Sleep)
> 
> They are optional methods, but if the BIOS supplies them,
> the OS is supposed to evaluate them immediately before
> writing the register to sleep, and immediately after waking up --
> a time when interrupts are disabled.
> 
> The spec says that they must be self-contained
> methods, not calling any other methods, perhaps
> because that they are run under unique conditions?
> 
> These methodds are evaluated in Linux by
> acpi_evaluate_object(), which always kmalloc's
> a return structure to conserve stack space.
> But kmalloc with interrupts off is problematic --
> do we really want to insist on GFP_ATOMIC here?

Well, I think we should.

Alternatively, we can keep a preallocated buffer for this purpose.

> Now, several years after ACPI 2.0 was released,
> we have yet to observe a single implementation of
> _GTS/_BFS in the field -- suggesting that they will
> never actually be deployed.
> 
> So lets keep Linux simple by removing this
> theoretical support for _GTS/_BFS, the only
> AML methods that mandated being evaluated
> with interrupts disabled.

I'm not sure if I agree with this approach.

My opinion is that we should be able to execute AML code with interrupts
disabled and there should be means to do that.

The entire irqrouter_resume() thing requires us to evaluate AML with interrupts
disabled and in that particular case it also really _makes_ _sense_.

So, IMO dropping _GTS/_BFS doesn't really buy us anything.

Thanks,
Rafael