On Tue, Mar 10, 2015 at 12:23:03PM +0000, Hanjun Guo wrote:

On 2015?03?07? 01:47, Lorenzo Pieralisi wrote:

quoted

On Wed, Feb 25, 2015 at 08:39:58AM +0000, Hanjun Guo wrote:

quoted

From: Al Stone <redacted>

ACPI reduced hardware mode is disabled by default, but ARM64
can only run properly in ACPI hardware reduced mode, so select
ACPI_REDUCED_HARDWARE_ONLY if ACPI is enabled on ARM64.

Agreed. This will remove unneeded acpica code. I think though,
you should also check the FADT flag HW_REDUCED_ACPI at boot to
make sure that the tables are HW reduced compliant. I am flagging

Agreed, I will add that check on top of this patch set. We explicitly
stated that we are using hardware reduced mode on ARM64 in the doc, so, 
how about print some warning message and go on with the boot if we
got the wrong flag HW_REDUCED_ACPI at boot?

Why would be boot if the ACPI tables are not HW_REDUCED_ACPI compliant ?

To look for trouble :) ? arm64 does not support any other ACPI model,
the missing flag should disable ACPI IMO on arm64.

You could add a check in this patch same place where you check
the FADT version and be done with this.

Thank you !
Lorenzo

quoted

this up because I noticed code in core code (not guarded by
ifdef) that checks:

acpi_gbl_reduced_hardware

and if it is not set it goes on instantiating fixed HW devices.

drivers/acpi/scan.c:2567

It is just a heads up, I think it is harmless, but one thing is
removing acpica code on ACPI HW reduced only, the other is to make
sure the kernel does not try to use ACPI HW features that acpica
can't support.

I agree, need some cleanups for the ACPICA code I think, and this
was raised about 1 and half years ago and Intel folks need more
consideration on that [1].

[1]: http://comments.gmane.org/gmane.linux.acpi.devel/63844

Thanks
Hanjun