本文基于RockPi 4A单板Linux4.4 内核介绍OPP Table。
内核中将频率、电压的相关配置放在DTSI文件中，这些配置信息组成的节点被称为OPP Table（Operating Performance Points）。
定义文件：arch/arm64/boot/dts/rockchip/rk3399-opp.dtsi,内容如下：
cluster0_opp: opp-table0 {
compatible = "operating-points-v2";
opp-shared;
rockchip,temp-hysteresis = <5000>; ## 5摄氏度
rockchip,low-temp = <0>;
rockchip,low-temp-min-volt = <900000>; ## 0.9V
nvmem-cells = <&cpul_leakage>;
nvmem-cell-names = "cpu_leakage";
rockchip,pvtm-voltage-sel = <
0 143500 0
143501 148500 1
148501 152000 2
152001 999999 3
>;
rockchip,pvtm-freq = <408000>;
rockchip,pvtm-volt = <1000000>;
rockchip,pvtm-ch = <0 0>;
rockchip,pvtm-sample-time = <1000>;
rockchip,pvtm-number = <10>;
rockchip,pvtm-error = <1000>;
rockchip,pvtm-ref-temp = <41>;
rockchip,pvtm-temp-prop = <115 66>;
rockchip,thermal-zone = "soc-thermal";
opp-408000000 {
opp-hz = /bits/ 64 <408000000>;
opp-microvolt = <800000 800000 1200000>;
opp-microvolt-L0 = <800000 800000 1200000>;
opp-microvolt-L1 = <800000 800000 1200000>;
opp-microvolt-L2 = <800000 800000 1200000>;
opp-microvolt-L3 = <800000 800000 1200000>;
clock-latency-ns = <40000>;
};
opp-600000000 {
opp-hz = /bits/ 64 <600000000>;
opp-microvolt = <800000 800000 1200000>;
opp-microvolt-L0 = <800000 800000 1200000>;
opp-microvolt-L1 = <800000 800000 1200000>;
opp-microvolt-L2 = <800000 800000 1200000>;
opp-microvolt-L3 = <800000 800000 1200000>;
clock-latency-ns = <40000>;
};
opp-816000000 {
opp-hz = /bits/ 64 <816000000>;
opp-microvolt = <850000 850000 1200000>;
opp-microvolt-L0 = <850000 850000 1200000>;
opp-microvolt-L1 = <825000 825000 1200000>;
opp-microvolt-L2 = <800000 800000 1200000>;
opp-microvolt-L3 = <800000 800000 1200000>;
clock-latency-ns = <40000>;
opp-suspend;
};
opp-1008000000 {
opp-hz = /bits/ 64 <1008000000>;
opp-microvolt = <925000 925000 1200000>;
opp-microvolt-L0 = <925000 925000 1200000>;
opp-microvolt-L1 = <900000 900000 1200000>;
opp-microvolt-L2 = <875000 875000 1200000>;
opp-microvolt-L3 = <850000 850000 1200000>;
clock-latency-ns = <40000>;
};
opp-1200000000 {
opp-hz = /bits/ 64 <1200000000>;
opp-microvolt = <1000000 1000000 1200000>;
opp-microvolt-L0 = <1000000 1000000 1200000>;
opp-microvolt-L1 = <975000 975000 1200000>;
opp-microvolt-L2 = <950000 950000 1200000>;
opp-microvolt-L3 = <925000 925000 1200000>;
clock-latency-ns = <40000>;
};
opp-1416000000 {
opp-hz = /bits/ 64 <1416000000>;
opp-microvolt = <1125000 1125000 1200000>;
opp-microvolt-L0 = <1125000 1125000 1200000>;
opp-microvolt-L1 = <1100000 1100000 1200000>;
opp-microvolt-L2 = <1075000 1075000 1200000>;
opp-microvolt-L3 = <1050000 1050000 1200000>;
clock-latency-ns = <40000>;
};
};
上面节点中的相关属性含义如下：
1、opp-shared：表示opp-table1是小核的各CPU共用。
2、rockchip,temp-hysteresis：迟滞参数，防止频繁进入高温或低温，单位：毫摄氏度。
3、rockchip,low-temp：低温阈值。小于该值时，进入低温，大于‘该值+迟滞参数’时，恢复常温。
4、rockchip,low-temp-min-volt：低温下最低电压，单位：微伏。
5、nvmem-cells：从eFUSE中读取相关信息值（小核漏电流）。
6、rockchip,pvtm-voltage-sel：min-pvtm（单位KHz）、max-pvtm（单位KHz）和voltage-selector(用于匹配opp节点中opp-microvolt-L*属性的序列号)。例：pvtm值为：0 ~ 143500 使用opp-microvolt-L0，143501 ~ 148500使用opp-microvolt-L1
7、rockchip,pvtm-freq：时钟频率（KHz），在获取pvtm的频率前，先设置CPU频率。
8、rockchip,pvtm-volt：电压（微伏），在获取pvtm的频率前，先设置CPU电压。
9、rockchip,pvtm-ch：PVTM通道，格式<通道号 sel的序号>
10、rockchip,pvtm-sample-time：PVTM采样时间，单位：毫秒。
11、rockchip,pvtm-number：PVTM采样个数。
12、rockchip,pvtm-error：允许采样数据之间的误差。
13、rockchip,pvtm-ref-temp：参考温度。
14、rockchip,pvtm-temp-prop：PVTM随温度变化的比例系数，格式<小于参考温度的比例系数 大于参考温度的比例系数>。
15、rockchip,thermal-zone：获取温度的thermal-zone。
16、opp-microvolt-L*：电压(微伏)，格式
17、clock-latency-ns：完成变频需要的时间，单位：纳秒。
在RK3399中，除了配置上述小核的opp table外，还设置了大核（cluster1_opp）、gpu(gpu_opp_table)等的相关值。查看命令如下：
root@linaro-alip:/sys/kernel/debug/opp# ls
cpu0 cpu1 cpu2 cpu3 cpu4 cpu5 opp_summary platform-ff9a0000.gpu
root@linaro-alip:/sys/kernel/debug/opp# cat opp_summary
device rate(Hz) target(uV) min(uV) max(uV)
-------------------------------------------------------------------
platform-ff9a0000.gpu
200000000 800000 800000 800000
300000000 800000 800000 800000
400000000 825000 825000 825000
600000000 925000 925000 925000
800000000 1100000 1100000 1100000
cpu4
408000000 800000 800000 1200000
600000000 800000 800000 1200000
816000000 825000 825000 1200000
1008000000 875000 875000 1200000
1200000000 950000 950000 1200000
1416000000 1025000 1025000 1200000
1608000000 1100000 1100000 1200000
1800000000 1200000 1200000 1200000
cpu0
408000000 800000 800000 1200000
600000000 800000 800000 1200000
816000000 850000 850000 1200000
1008000000 925000 925000 1200000
1200000000 1000000 1000000 1200000
1416000000 1125000 1125000 1200000
注：
CPU PVTM(Process Voltage Temperature Monitor)是一个位于CPU附近，能反应出不同芯片之间性能差异的模块，受工艺，电压和温度 的影响。
参考：
Documentation/devicetree/bindings/cpufreq/cpufreq-rockchip.txt
Documentation/devicetree/bindings/cpufreq/cpufreq-rockchip.txt