Re: [PATCH v5 1/5] ACPI: introduce CONFIG_ACPI_REDUCED_HARDWARE_ONLY to enforce this ACPI mode

[Catalin Marinas <catalin.marinas@arm.com>]

On Thu, Jan 09, 2014 at 09:20:23PM +0000, Al Stone wrote:
> On 01/09/2014 10:38 AM, Catalin Marinas wrote:
> > On 8 January 2014 12:46, Arnd Bergmann <arnd@arndb.de> wrote:
> >> On Wednesday 08 January 2014, al.stone@linaro.org wrote:
> >>> Even though support for X86 in hardware reduced mode is possible, it
> >>> is NOT enabled.  Extensive effort has gone into the Linux kernel so that
> >>> there is a single kernel image than can run on all x86 hardware; the kernel
> >>> changes run-time behavior to adapt to the hardware being used.  This is not
> >>> currently possible with the existing ACPICA infrastructure but only presents
> >>> a problem on achitectures supporting both hardware-reduced and legacy modes
> >>> of ACPI -- i.e., on x86 only.
> >>
> >> Not sure about the logic here: While it's certainly possible to build a kernel
> >> that runs on all x86 machines, it's also possible to build one that only
> >> runs on some of them when some basic options are turned off. I don't see
> >> any difference between that and what we have on ARM64 or the multiplatform
> >> subset of ARM32.
> >
> > Would we ever need !CONFIG_ACPI_REDUCED_HARDWARE_ONLY on ARM or ARM64?
> > If not, we could even make this always on for these archs.
> >
> 
> Not that I know of -- and I would hope not.  This mode is so much
> more straightforward that it makes no sense to me to do anything
> but reduced HW if you have the choice.

Thanks for clarifying.

> I assume you were thinking of something like this in the arch Kconfig
> file:
> 
> config ARM64
> 	....
> 	select ACPI_REDUCED_HARDWARE_ONLY if ACPI
> 	...
> 
> But, do let me know if you had something else in mind.  I think it does
> make sense to add so I'll put this in the next version.

The change makes sense but I think it should come with the patches for
ACPI support on arm64 rather than your hw-reduced patches.

-- 
Catalin