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diff --git a/Documentation/devicetree/bindings/cpu/cpu-capacity.txt b/Documentation/devicetree/bindings/cpu/cpu-capacity.txt new file mode 100644 index 000000000000..f28e1adad428 --- /dev/null +++ b/Documentation/devicetree/bindings/cpu/cpu-capacity.txt @@ -0,0 +1,238 @@ +========================================== +CPU capacity bindings +========================================== + +========================================== +1 - Introduction +========================================== + +Some systems may be configured to have cpus with different power/performance +characteristics within the same chip. In this case, additional information has +to be made available to the kernel for it to be aware of such differences and +take decisions accordingly. + +========================================== +2 - CPU capacity definition +========================================== + +CPU capacity is a number that provides the scheduler information about CPUs +heterogeneity. Such heterogeneity can come from micro-architectural differences +(e.g., ARM big.LITTLE systems) or maximum frequency at which CPUs can run +(e.g., SMP systems with multiple frequency domains). Heterogeneity in this +context is about differing performance characteristics; this binding tries to +capture a first-order approximation of the relative performance of CPUs. + +CPU capacities are obtained by running a suitable benchmark. This binding makes +no guarantees on the validity or suitability of any particular benchmark, the +final capacity should, however, be: + +* A "single-threaded" or CPU affine benchmark +* Divided by the running frequency of the CPU executing the benchmark +* Not subject to dynamic frequency scaling of the CPU + +For the time being we however advise usage of the Dhrystone benchmark. What +above thus becomes: + +CPU capacities are obtained by running the Dhrystone benchmark on each CPU at +max frequency (with caches enabled). The obtained DMIPS score is then divided +by the frequency (in MHz) at which the benchmark has been run, so that +DMIPS/MHz are obtained. Such values are then normalized w.r.t. the highest +score obtained in the system. + +========================================== +3 - capacity-dmips-mhz +========================================== + +capacity-dmips-mhz is an optional cpu node [1] property: u32 value +representing CPU capacity expressed in normalized DMIPS/MHz. At boot time, the +maximum frequency available to the cpu is then used to calculate the capacity +value internally used by the kernel. + +capacity-dmips-mhz property is all-or-nothing: if it is specified for a cpu +node, it has to be specified for every other cpu nodes, or the system will +fall back to the default capacity value for every CPU. If cpufreq is not +available, final capacities are calculated by directly using capacity-dmips- +mhz values (normalized w.r.t. the highest value found while parsing the DT). + +=========================================== +4 - Examples +=========================================== + +Example 1 (ARM 64-bit, 6-cpu system, two clusters): +The capacities-dmips-mhz or DMIPS/MHz values (scaled to 1024) +are 1024 and 578 for cluster0 and cluster1. Further normalization +is done by the operating system based on cluster0@max-freq=1100 and +cluster1@max-freq=850, final capacities are 1024 for cluster0 and +446 for cluster1 (578*850/1100). + +cpus { + #address-cells = <2>; + #size-cells = <0>; + + cpu-map { + cluster0 { + core0 { + cpu = <&A57_0>; + }; + core1 { + cpu = <&A57_1>; + }; + }; + + cluster1 { + core0 { + cpu = <&A53_0>; + }; + core1 { + cpu = <&A53_1>; + }; + core2 { + cpu = <&A53_2>; + }; + core3 { + cpu = <&A53_3>; + }; + }; + }; + + idle-states { + entry-method = "psci"; + + CPU_SLEEP_0: cpu-sleep-0 { + compatible = "arm,idle-state"; + arm,psci-suspend-param = <0x0010000>; + local-timer-stop; + entry-latency-us = <100>; + exit-latency-us = <250>; + min-residency-us = <150>; + }; + + CLUSTER_SLEEP_0: cluster-sleep-0 { + compatible = "arm,idle-state"; + arm,psci-suspend-param = <0x1010000>; + local-timer-stop; + entry-latency-us = <800>; + exit-latency-us = <700>; + min-residency-us = <2500>; + }; + }; + + A57_0: cpu@0 { + compatible = "arm,cortex-a57"; + reg = <0x0 0x0>; + device_type = "cpu"; + enable-method = "psci"; + next-level-cache = <&A57_L2>; + clocks = <&scpi_dvfs 0>; + cpu-idle-states = <&CPU_SLEEP_0 &CLUSTER_SLEEP_0>; + capacity-dmips-mhz = <1024>; + }; + + A57_1: cpu@1 { + compatible = "arm,cortex-a57"; + reg = <0x0 0x1>; + device_type = "cpu"; + enable-method = "psci"; + next-level-cache = <&A57_L2>; + clocks = <&scpi_dvfs 0>; + cpu-idle-states = <&CPU_SLEEP_0 &CLUSTER_SLEEP_0>; + capacity-dmips-mhz = <1024>; + }; + + A53_0: cpu@100 { + compatible = "arm,cortex-a53"; + reg = <0x0 0x100>; + device_type = "cpu"; + enable-method = "psci"; + next-level-cache = <&A53_L2>; + clocks = <&scpi_dvfs 1>; + cpu-idle-states = <&CPU_SLEEP_0 &CLUSTER_SLEEP_0>; + capacity-dmips-mhz = <578>; + }; + + A53_1: cpu@101 { + compatible = "arm,cortex-a53"; + reg = <0x0 0x101>; + device_type = "cpu"; + enable-method = "psci"; + next-level-cache = <&A53_L2>; + clocks = <&scpi_dvfs 1>; + cpu-idle-states = <&CPU_SLEEP_0 &CLUSTER_SLEEP_0>; + capacity-dmips-mhz = <578>; + }; + + A53_2: cpu@102 { + compatible = "arm,cortex-a53"; + reg = <0x0 0x102>; + device_type = "cpu"; + enable-method = "psci"; + next-level-cache = <&A53_L2>; + clocks = <&scpi_dvfs 1>; + cpu-idle-states = <&CPU_SLEEP_0 &CLUSTER_SLEEP_0>; + capacity-dmips-mhz = <578>; + }; + + A53_3: cpu@103 { + compatible = "arm,cortex-a53"; + reg = <0x0 0x103>; + device_type = "cpu"; + enable-method = "psci"; + next-level-cache = <&A53_L2>; + clocks = <&scpi_dvfs 1>; + cpu-idle-states = <&CPU_SLEEP_0 &CLUSTER_SLEEP_0>; + capacity-dmips-mhz = <578>; + }; + + A57_L2: l2-cache0 { + compatible = "cache"; + }; + + A53_L2: l2-cache1 { + compatible = "cache"; + }; +}; + +Example 2 (ARM 32-bit, 4-cpu system, two clusters, + cpus 0,1@1GHz, cpus 2,3@500MHz): +capacities-dmips-mhz are scaled w.r.t. 2 (cpu@0 and cpu@1), this means that first +cpu@0 and cpu@1 are twice fast than cpu@2 and cpu@3 (at the same frequency) + +cpus { + #address-cells = <1>; + #size-cells = <0>; + + cpu0: cpu@0 { + device_type = "cpu"; + compatible = "arm,cortex-a15"; + reg = <0>; + capacity-dmips-mhz = <2>; + }; + + cpu1: cpu@1 { + device_type = "cpu"; + compatible = "arm,cortex-a15"; + reg = <1>; + capacity-dmips-mhz = <2>; + }; + + cpu2: cpu@2 { + device_type = "cpu"; + compatible = "arm,cortex-a15"; + reg = <0x100>; + capacity-dmips-mhz = <1>; + }; + + cpu3: cpu@3 { + device_type = "cpu"; + compatible = "arm,cortex-a15"; + reg = <0x101>; + capacity-dmips-mhz = <1>; + }; +}; + +=========================================== +5 - References +=========================================== + +[1] ARM Linux Kernel documentation - CPUs bindings + Documentation/devicetree/bindings/arm/cpus.yaml |