On 09/12/2014 04:03 PM, Graeme Gregory wrote:

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

quoted

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.

                                                    ^ meant C/P sorry

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

Correct. In replying to the above, I was thinking about power and
performance management of components  - CPU (C/P), and device (D)
specific power/performance states - not the overall system (S) state,
and I went off on a tangent. That was off-topic. For the actual topic at
hand, that of global sleep, you are correct that only G0 (S0) and S5 are
really defined today. Though I do think that the PCC might be used to
actually implement overall system sleep state transitions later.

Jon.