On Tue, Dec 9, 2014 at 9:51 AM, Viresh Kumar viresh.kumar@linaro.org wrote:
On 4 December 2014 at 16:44, Viresh Kumar viresh.kumar@linaro.org wrote:
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.?
Some updates on the structure of bindings which I got up to with help of Arnd and Rob over IRC, have got better examples to show how things would look like:
diff --git a/Documentation/devicetree/bindings/power/opp.txt b/Documentation/devicetree/bindings/power/opp.txt index 74499e5033fc..8ae574b84650 100644 --- a/Documentation/devicetree/bindings/power/opp.txt +++ b/Documentation/devicetree/bindings/power/opp.txt @@ -1,9 +1,292 @@ -* Generic OPP Interface +Generic OPP (Operating Performance Points) Interface +----------------------------------------------------
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.
+opp nodes and opp-lists
+- opp-listN:
- List of nodes defining performance points. Following belong to the nodes
- within the opp-lists.
- Required properties:
- frequency-kHz: Frequency in kHz
s/kHz/khz/
- voltage-uV: voltage in micro Volts
-microvolt is more consistent with regulator binding.
The names are a bit redundant. perhaps opp-khz and opp-microvolt instead.
- Optional properties:
- turbo-mode: Marks the volt-freq pair as turbo pair.
- status: Marks the node enabled/disabled.
+- oppN:
- Operating performance point node per device. Devices using it should have its
- phandle in their "operating-points-v2" property.
- Required properties:
- compatible: allow OPPs to express their compatibility
- 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 1: Simple case of dual-core cortex A9-single cluster, sharing clock line.
+/ {
cpus {#address-cells = <1>;#size-cells = <0>;cpu@0 {compatible = "arm,cortex-a9";reg = <0>;next-level-cache = <&L2>;operating-points-v2 = <&opp0>;opp0: opp0 {
I don't really like having this under cpu0 when it applies to all cpus. I would move it out of /cpus.
compatible = "linux,cpu-dvfs";
This should not be linux specific. Probably not cpu specific either.
clocks = <&clk-controller 0>;clock-names = "cpu";
clocks are an input to the cpu, not really an opp. You could have a an OPP which uses a different parent clock, but that is most likely a switch within the clock controller rather than 2 clock inputs to the cpu.
I think the clock binding for cpus should stand on its own independent of OPPs.
opp-supply = <&cpu-supply0>;
Same comment as clocks applies here.
voltage-tolerance = <2>; /* percentage */clock-latency = <300000>;
These could be per entry. I'm not sure it is worth the savings to not just always specify them per entry.
We should append units (-us) to clock-latency unless there is a good reason to maintain compatibility.
opp-list = <&opplist0>;
With the above changes, having this list is unnecessary.
So, what I envision is like this:
/cpus { cpu@0 { clocks = <...>; cpu-supply = <...>; operating-point-v2 = <&cpu0-opp>; }; cpu@1 { clocks = <...>; cpu-supply = <...>; operating-point-v2 = <&cpu1-opp>; }; };
cpu0-opp : opp0 { compatible = "operating-point-table"; entry0 { opp-khz = <500000>; opp-microvolt = <900000>; }; entry1 { opp-khz = <1000000>; opp-microvolt = <1000000>; turbo-mode; }; };
cpu1-opp : opp1 { compatible = "operating-point-table"; ... };
We need to also consider if this all works for other non-cpu OPPs like GPUs or DRAM/bus.
Rob