Re: [PATCH V3 1/2] ACPI / EC: Fix broken big-endian 64bit platforms using 'global_lock'

Arnd Bergmann
2015-09-23T09:39:14Z

On Wednesday 23 September 2015 10:15:42 Sudeep Holla wrote:
> On 15/09/15 09:34, Viresh Kumar wrote:
> > global_lock is defined as an unsigned long and accessing only its lower
> > 32 bits from sysfs is incorrect, as we need to consider other 32 bits
> > for big endian 64 bit systems.
> >
> > Fix that by making global_lock an u32 instead.
> >
> > Cc: <stable@vger.kernel.org> # v4.1+
> > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> >
> > ---
> > Its marked just for # v4.1+, because arm64 has the first 64 big-endian
> > platform with ACPI. And ACPI support for that is mainlined recently
> > only (Arnd Bergmann).
> >
>
> Just to clarify, we don't support big-endian with ACPI on ARM64.
> We mandate use of EFI for ACPI on ARM64 and EFI spec mandates only
> little endian.
>

EFI doesn't care what endianess the kernel has, as long as the
data structures are interpreted in the same way that the firmware
defines them, and I thought that at least UEFI on ARM64 with big-endian
is working in principle (if not, that is a bug that should be fixed).

If ACPI is broken with big-endian kernels, we should probably add a
Kconfig statement to forbid it, like this:

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 5d1015c26ff4..06cacc13e3d2 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -6,6 +6,7 @@ menuconfig ACPI
bool "ACPI (Advanced Configuration and Power Interface) Support"
depends on !IA64_HP_SIM
depends on IA64 || X86 || (ARM64 && EXPERT)
+ depends on !ARM64 || !CPU_BIG_ENDIAN || BROKEN
depends on PCI
select PNP
default y

Arnd