Hi Rob, et al..
Current OPP (Operating performance point) DT bindings are proven to be insufficient at multiple instances.
There had been multiple band-aid approaches to get them fixed (The latest one being: http://www.mail-archive.com/devicetree@vger.kernel.org/msg53398.html). For obvious reasons Rob rejected them and shown the right path forward. And this is the first try to get those with a pen and paper.
The shortcomings we are trying to solve here:
- Some kind of compatibility string to probe the right cpufreq driver for platforms, when multiple drivers are available. For example: how to choose between cpufreq-dt and arm_big_little drivers.
- Getting clock sharing information between CPUs. Single shared clock vs. independent clock per core vs. shared clock per cluster.
- Support for turbo modes
- Other per OPP settings: transition latencies, disabled status, etc.?
The below document should be enough to describe how I am trying to fix these. Please let me know what all I need to fix, surely there would be lots of obstacles. I am prepared to get beaten up :)
I accept in advance that naming is extremely bad here, I need some suggestions for sure.
Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- Documentation/devicetree/bindings/power/opp.txt | 147 ++++++++++++++++++++++++ 1 file changed, 147 insertions(+)
diff --git a/Documentation/devicetree/bindings/power/opp.txt b/Documentation/devicetree/bindings/power/opp.txt index 74499e5..5efd8d4 100644 --- a/Documentation/devicetree/bindings/power/opp.txt +++ b/Documentation/devicetree/bindings/power/opp.txt @@ -4,6 +4,153 @@ SoCs have a standard set of tuples consisting of frequency and voltage pairs that the device will support per voltage domain. These are called Operating Performance Points or OPPs.
+This documents defines OPP bindings with its required/optional properties. +OPPs can be defined for any device, this file uses CPU device as an example to +illustrate how to define OPPs. + +linux,operating-points, opp-lists and opps: + +- linux,operating-points: + Container of all OPP nodes. + + Required properties: + - opp nodes (explained below) + + Optional properties: + - compatible: allow OPPs to express their compatibility with devices + + +- opp-list@*: + List of nodes defining performance points. Following belong to the nodes + within the opp-lists. + + Required properties: + - frequency-kHz: Frequency in kHz + - voltage-uV: voltage in micro Volts + + Optional properties: + - turbo-mode: Marks the volt-freq pair as turbo pair. + - status: Marks the node enabled/disabled. + + +- opp@*: + Operating performance point node per device. Multiple devices sharing it can + use its phandle in their 'opp' property. + + Required properties: + - opp-list: phandle to opp-list defined above. + + Optional properties: + - clocks: Tuple of clock providers + - clock-names: Clock names + - opp-supply: phandle to the parent supply/regulator node + - voltage-tolerance: Specify the CPU voltage tolerance in percentage. + - clock-latency: Specify the possible maximum transition latency for clock, + in unit of nanoseconds. + +Example: Multi-cluster system with separate clock lines for clusters. All CPUs + in the clusters share same clock lines. + +/ { + cpus { + #address-cells = <1>; + #size-cells = <0>; + + linux,operating-points { + compatible = "linux,cpufreq-dt"; + + opp-list0: opp-list@0 { + { + frequency-kHz = <1000000>; + voltage-uV = <975000>; + status = "okay"; + }; + { + frequency-kHz = <1100000>; + voltage-uV = <1000000>; + status = "okay"; + }; + { + frequency-kHz = <1200000>; + voltage-uV = <1025000>; + status = "okay"; + turbo-mode; + }; + }; + + opp-list1: opp-list@1 { + { + frequency-kHz = <1300000>; + voltage-uV = <1050000>; + status = "okay"; + }; + { + frequency-kHz = <1400000>; + voltage-uV = <1075000>; + status = "disabled"; + }; + { + frequency-kHz = <1500000>; + voltage-uV = <1100000>; + status = "okay"; + turbo-mode; + }; + }; + + opp0: opp@0 { + clocks = <&clk-controller 0>; + clock-names = "cpu"; + opp-supply = <&cpu-supply0>; + voltage-tolerance = <2>; /* percentage */ + clock-latency = <300000>; + opp-list = <&opp-list0>; + }; + + opp1: opp@1 { + clocks = <&clk-controller 1>; + clock-names = "cpu"; + opp-supply = <&cpu-supply1>; + voltage-tolerance = <2>; /* percentage */ + clock-latency = <400000>; + opp-list = <&opp-list1>; + }; + }; + + cpu@0 { + compatible = "arm,cortex-a7"; + reg = <0>; + next-level-cache = <&L2>; + opps = <opp0>; + }; + + cpu@1 { + compatible = "arm,cortex-a7"; + reg = <1>; + next-level-cache = <&L2>; + opps = <opp0>; + }; + + cpu@100 { + compatible = "arm,cortex-a15"; + reg = <100>; + next-level-cache = <&L2>; + opps = <opp1>; + }; + + cpu@101 { + compatible = "arm,cortex-a15"; + reg = <101>; + next-level-cache = <&L2>; + opps = <opp1>; + }; + }; +}; + + + +Deprecated Bindings +------------------- + Properties: - operating-points: An array of 2-tuples items, and each item consists of frequency and voltage like <freq-kHz vol-uV>.