Re: [PATCH] ACPI / ARM64: Remove EXPERT dependency for ACPI on ARM64

Rafael J. Wysocki
2016-03-31T12:47:41Z

On Thu, Mar 31, 2016 at 2:36 PM, Will Deacon <will.deacon@arm.com> wrote:
> On Thu, Mar 31, 2016 at 02:04:05PM +0200, Rafael J. Wysocki wrote:
>> On Thu, Mar 31, 2016 at 5:44 AM, Hanjun Guo <guohanjun@huawei.com> wrote:
>> > On 2016/3/31 1:58, Mark Brown wrote:
>> >> When ACPI was originally merged for arm64 it had only been tested on
>> >> emulators and not on real physical platforms and no platforms were
>> >> relying on it. This meant that there were concerns that there might be
>> >> serious issues attempting to use it on practical systems so it had a
>> >> dependency on EXPERT added to warn people that it was in an early stage
>> >> of development with very little practical testing. Since then things
>> >> have moved on a bit. We have seen people testing on real hardware and
>> >> now have people starting to produce some platforms (the most prominent
>> >> being the 96boards Cello) which only have ACPI support and which build
>> >> and run to some useful extent with mainline.
>> >>
>> >> This is not to say that ACPI support or support for these systems is
>> >> completely done, there are still areas being worked on such as PCI, but
>> >> at this point it seems that we can be reasonably sure that ACPI will be
>> >> viable for use on ARM64 and that the already merged support works for
>> >> the cases it handles. For the AMD Seattle based platforms support
>> >> outside of PCI has been fairly complete in mainline a few releases now.
>> >>
>> >> This is also not to say that we don't have vendors working with ACPI who
>> >> are trying do things that we would not consider optimal but it does not
>> >> appear that the EXPERT dependency is having a substantial impact on
>> >> these vendors.
>> >>
>> >> Given all this it seems that at this point the EXPERT dependency mainly
>> >> creates inconvenience for users with systems that are doing the right
>> >> thing and gets in the way of including the ACPI code in the testing that
>> >> people are doing on mainline. Removing it should help our ongoing
>> >> testing cover those platforms with only ACPI support and help ensure
>> >> that when ACPI code is merged any problems it causes for other users are
>> >> more easily discovered.
>> >>
>> >> Signed-off-by: Mark Brown <broonie@kernel.org>
>> >
>> > Acked-by: Hanjun Guo <hanjun.guo@linaro.org>
>> >
>> >> ---
>> >> drivers/acpi/Kconfig | 2 +-
>> >> 1 file changed, 1 insertion(+), 1 deletion(-)
>> >>
>> >> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
>> >> index 82b96ee8624c..bf5dc1ac3446 100644
>> >> --- a/drivers/acpi/Kconfig
>> >> +++ b/drivers/acpi/Kconfig
>> >> @@ -5,7 +5,7 @@
>> >> menuconfig ACPI
>> >> bool "ACPI (Advanced Configuration and Power Interface) Support"
>> >> depends on !IA64_HP_SIM
>> >> - depends on IA64 || X86 || (ARM64 && EXPERT)
>> >> + depends on IA64 || X86 || ARM64
>> >> depends on PCI
>> >> select PNP
>> >> default y
>>
>> OK
>>
>> What do the ARM64 maintainers think?
>
> I'm unsure about whether or not we want 'default y' here, but I'd like
> to wait for Catalin to come back from his 2-week holiday before going
> anywhere with this patch. It's only fair that his opinion should be
> taken into account, and there's not a huge rush for this. I do consider
> "ACPI-only platforms" as simply "platforms without a .dtb" (modulo
> any significant AML code) and therefore don't view this as a blocking
> issue.
>
> We should also take into account the large amount of ongoing ACPI work
> (e.g. the DSD and PRP0001 saga, PCI and IORT support, virtualisation work,
> etc), and decide whether or not that's currently in a state where we want
> to encourage people to start using this in their arm64 kernels.

Fair enough.