From mboxrd@z Thu Jan 1 00:00:00 1970 From: jcm@redhat.com (Jon Masters) Date: Fri, 12 Sep 2014 17:10:32 -0400 Subject: [PATCH v4 05/18] ARM64 / ACPI: Introduce sleep-arm.c In-Reply-To: <20140912200355.GD9234@xora-haswell.xora.org.uk> References: <1410530416-30200-1-git-send-email-hanjun.guo@linaro.org> <1410530416-30200-6-git-send-email-hanjun.guo@linaro.org> <54134CE8.8070506@redhat.com> <20140912200355.GD9234@xora-haswell.xora.org.uk> Message-ID: <54136148.40106@redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 09/12/2014 04:03 PM, Graeme Gregory wrote: > On Fri, Sep 12, 2014 at 03:43:36PM -0400, Jon Masters wrote: >> On 09/12/2014 10:00 AM, Hanjun Guo wrote: >>> From: Graeme Gregory >>> >>> 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.