From c4fc9baf447062d1e6c6bb2d97c6d0d714fdc666 Mon Sep 17 00:00:00 2001 From: Stewart Smith Date: Wed, 28 Jan 2015 18:58:31 +1100 Subject: Add skeleton documentation on power-mgt section of device-tree Signed-off-by: Stewart Smith --- doc/device-tree/ibm,opal/power-mgt.txt | 51 ++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 doc/device-tree/ibm,opal/power-mgt.txt (limited to 'doc') diff --git a/doc/device-tree/ibm,opal/power-mgt.txt b/doc/device-tree/ibm,opal/power-mgt.txt new file mode 100644 index 0000000..d67c1b3 --- /dev/null +++ b/doc/device-tree/ibm,opal/power-mgt.txt @@ -0,0 +1,51 @@ +ibm,opal/power-mgt device tree entries +-------------------------------------- + +All available CPU idle states are listed in ibm,cpu-idle-state-names + +For example: +ibm,cpu-idle-state-names = "nap", "fastsleep_", "winkle"; + +The idle states are characterized by latency and residency +numbers which determine the breakeven point for entry into them. The +latency is a measure of the exit overhead from the idle state and +residency is the minimum amount of time that a CPU must be predicted +to be idle so as to reap the powersavings from entering into that idle +state. + +These numbers are made use of by the cpuidle governors in the kernel to +arrive at the appropriate idle state that a CPU must enter into when there is +no work to be done. The values in ibm,cpu-idle-state-latencies-ns are the +the measured latency numbers for the idle states. The residency numbers have +been arrived at experimentally after ensuring that the performance of latency +sensitive workloads do not regress while allowing deeper idle states to be +entered into during low load situations. The kernel is expected to use these +values for optimal power efficiency. + +ibm,cpu-idle-state-residency-ns = <0x1 0x2 0x3> +ibm,cpu-idle-state-latencies-ns = <0x1 0x2 0x3> + +ibm,pstate-vcss ibm,pstate-vdds +------------------------------- + +During characterisation, we'd like to allow userspace to see the vdd and +vcs values exposed by the OCC. This change adds two new properties to +expose these: + + ibm,pstate-vdds + ibm,pstate-vcss + +- containing one byte per pstate, representing the Vdd or Vcs value for + that pstate. + + +FIXME: document these: +ibm,cpu-idle-state-flags +ibm,cpu-idle-state-names +ibm,cpu-idle-state-pmicr +ibm,cpu-idle-state-pmicr-mask +ibm,pstate-frequencies-mhz +ibm,pstate-ids +ibm,pstate-max +ibm,pstate-min +ibm,pstate-nominal -- cgit v1.1