On Fri, Sep 12, 2014 at 03:43:36PM -0400, Jon Masters wrote:

On 09/12/2014 10:00 AM, Hanjun Guo wrote:

quoted

From: Graeme Gregory <redacted>

ACPI 5.1 does not currently support S states for ARM64 hardware but
ACPI code will call acpi_target_system_state() for device power
managment, so introduce sleep-arm.c to allow other drivers to function
until S states are defined.

Aside: ACPI5.1 does define the Platform Communication Channel and CPC
(Collaborative Processor Performance Control). Some details need to be
fleshed out there for practical 64-bit ARMv8 server systems, but the
underpinnings and mechanisms are in place in the 5.1 specification that
can be built upon over time to achieve practical S-State equivalence.

Disagree, S-States are about going to sleep or hibernating, that is
nothing to do with CPU Performance.

Graeme