build_embed_linux_system

系统时钟和OPP管理模块

cpufreq模块的主要功能是动态调整CPU的频率和电压，以在性能和功耗之间取得平衡，OPP结构允许系统根据负载需求动态调整设备的性能和功耗，以实现更高的能效。cpufreq模块负责动态调整CPU的频率和电压，而opp模块则提供了描述设备性能状态的机制，并为cpufreq模块提供了调频调压所需的频率和电压信息。这两个模块共同协作，实现了Linux内核中的动态电源管理和性能调节功能。在日常开发中，主要通过应用层的接口去完成对cpu电压和频率管理，支持的配置文件如下所示。

# 应用层访问处理
/sys/devices/system/cpu/cpu0/cpufreq                                # 设备时钟平吕管理目录
/sys/bus/cpu/devices/cpu0/                                          # 对设备路径的引用
/sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq               # 当前的内核设定的时钟频率
/sys/devices/system/cpu/cpu0/cpufreq/scaling_driver                 # 处理时钟的驱动名称
/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor               # 当前的cpu工作模式
/sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq               # 设备允许的最大时钟
/sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq               # 设备允许的最小时钟
/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies  # 可配置的主时钟频率
/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors    # 可配置的主频工作模式
    conservative - 保守模式，不支持高频运行
    userspace - 用户态应用程序管理模式，用户编辑配置文件修改频率
    powersave - 低功耗模式，系统尽可能以低频运行
    performance - 高性能模式，系统尽可能以最高允许频率运行
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq               # 从CPU中读取的真实时钟频率
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq               # 从CPU中读取的真实允许最大时钟频率
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq               # 从CPU中读取的真实允许最小时钟频率
/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_transition_latency     # cpu发生频率切换时所需要的最小时间

相关文件。

drivers/cpufreq/imx6q-cpufreq.c     //管理imx6ull时钟的接口
drivers/opp/of.c                    //系统管理opp的接口
drivers/opp/core.c

freq_cpu

对于imx6ull设备，通过drivers/cpufreq目录下的驱动文件获取设备树中的频率，其中设备树格式如下。

&cpu0 {
    //......
    operating-points = <
        /* kHz    uV */
        900000    1275000
        792000    1225000
        696000    1175000
        528000    1175000
        396000    1025000
        198000    950000
    >;  // operationg-points定义系统opp支持的时钟频率列表
    fsl,soc-operating-points = <
        /* KHz    uV */
        900000    1250000
        792000    1175000
        696000    1175000
        528000    1175000
        396000    1175000
        198000    1175000
    >;  // fsl,soc-operating-points定义nxp私有的支持的时钟频率列表
};

在内核中，通过imx6q-cpufreq.c解析设备树获取支持的频率，电压范围。

//imx6ull管理时钟频率的实现
drivers/cpufreq/imx6q-cpufreq.c

// drivers/cpufreq/imx6q-cpufreq.c
// imx6q_cpufreq_probe 
// 设置cpufreq时钟关键函数
static int imx6q_cpufreq_probe(struct platform_device *pdev)
{
    //.....

    //根据设备树cpu节点的operating-points节点，生成支持的"频率-电压"管理的opp表格
    ret = dev_pm_opp_of_add_table(cpu_dev);
    if (ret < 0) {
        dev_err(cpu_dev, "failed to init OPP table: %d\n", ret);
        goto put_reg;
    }

    //根据cpu标签型号，对于支持的频率-电压的opp表格进行裁剪
    if (of_machine_is_compatible("fsl,imx6ul") ||
        of_machine_is_compatible("fsl,imx6ull")) {
        ret = imx6ul_opp_check_speed_grading(cpu_dev);
    } else {
        ret = imx6q_opp_check_speed_grading(cpu_dev);
    }
    if (ret) {
        dev_err_probe(cpu_dev, ret, "failed to read ocotp\n");
        goto out_free_opp;
    }

    //获取处理后表格中的总项数
    num = dev_pm_opp_get_opp_count(cpu_dev);
    if (num < 0) {
        ret = num;
        dev_err(cpu_dev, "no OPP table is found: %d\n", ret);
        goto out_free_opp;
    }

    //读取此时的opp表格，写入到freq_table中
    //此表格中第一行为最低频率-最低电压，最后一行为最高频率-最高电压
    ret = dev_pm_opp_init_cpufreq_table(cpu_dev, &freq_table);
    if (ret) {
        dev_err(cpu_dev, "failed to init cpufreq table: %d\n", ret);
        goto out_free_opp;
    }

    //...

    //获取nxp自定义的电压-频率列表资源，比对处理，保存到imx6_soc_volt列表中
    prop = of_find_property(np, "fsl,soc-operating-points", NULL);
    if (!prop || !prop->value)
        goto soc_opp_out;

    nr = prop->length / sizeof(u32);
    if (nr % 2 || (nr / 2) < num)
        goto soc_opp_out;

    for (j = 0; j < num; j++) {
        val = prop->value;
        for (i = 0; i < nr / 2; i++) {
            unsigned long freq = be32_to_cpup(val++);
            unsigned long volt = be32_to_cpup(val++);
            if (freq_table[j].frequency == freq) {
                imx6_soc_volt[soc_opp_count++] = volt;
                break;
            }
        }
        dev_err(cpu_dev, "freq:%d\n", freq_table[j].frequency);
    }

soc_opp_out:
    /* use fixed soc opp volt if no valid soc opp info found in dtb */
    if (soc_opp_count != num) {
        dev_warn(cpu_dev, "can NOT find valid fsl,soc-operating-points property in dtb, use default value!\n");
        for (j = 0; j < num; j++)
            imx6_soc_volt[j] = PU_SOC_VOLTAGE_NORMAL;
        if (freq_table[num - 1].frequency * 1000 == FREQ_1P2_GHZ)
            imx6_soc_volt[num - 1] = PU_SOC_VOLTAGE_HIGH;
    }

    //...
    
    // OPP要求处理后为频率增加的有序表格，则位置0频率最小，位置1频率最大
    // 可以通过此方法获取最大最小频率，然后获取最大最小电压
    max_freq = freq_table[--num].frequency;
    opp = dev_pm_opp_find_freq_exact(cpu_dev,
                  freq_table[0].frequency * 1000, true);
    min_volt = dev_pm_opp_get_voltage(opp);
    dev_pm_opp_put(opp);
    opp = dev_pm_opp_find_freq_exact(cpu_dev, max_freq * 1000, true);
    max_volt = dev_pm_opp_get_voltage(opp);
    dev_pm_opp_put(opp);

    // 设置内核允许的最大最小电压，用于保护
    ret = regulator_set_voltage_time(arm_reg, min_volt, max_volt);
    if (ret > 0)
        transition_latency += ret * 1000;

    //注册cpufreq时钟驱动
    ret = cpufreq_register_driver(&imx6q_cpufreq_driver);
    if (ret) {
        dev_err(cpu_dev, "failed register driver: %d\n", ret);
        goto free_freq_table;
    }

    //...
}

// imx6ul_opp_check_speed_grading 
// 检查处理时钟的函数
#define OCOTP_CFG3_6UL_SPEED_696MHZ    0x2
#define OCOTP_CFG3_6ULL_SPEED_792MHZ    0x2
#define OCOTP_CFG3_6ULL_SPEED_900MHZ    0x3

static int imx6ul_opp_check_speed_grading(struct device *dev)
{
    u32 val;
    int ret = 0;

    // 通过读取speed_grade，获取speed grading配置
    if (of_find_property(dev->of_node, "nvmem-cells", NULL)) {
        ret = nvmem_cell_read_u32(dev, "speed_grade", &val);
        if (ret)
            return ret;
    } else {
        struct device_node *np;
        void __iomem *base;

        np = of_find_compatible_node(NULL, NULL, "fsl,imx6ul-ocotp");
        if (!np)
            np = of_find_compatible_node(NULL, NULL,
                                "fsl,imx6ull-ocotp");
        if (!np)
            return -ENOENT;

        base = of_iomap(np, 0);
        of_node_put(np);
        if (!base) {
            dev_err(dev, "failed to map ocotp\n");
            return -EFAULT;
        }

        val = readl_relaxed(base + OCOTP_CFG3);
        iounmap(base);
    }

    /*
     * Speed GRADING[1:0] defines the max speed of ARM:
     * 2b'00: Reserved;
     * 2b'01: 528000000Hz;
     * 2b'10: 696000000Hz on i.MX6UL, 792000000Hz on i.MX6ULL;
     * 2b'11: 900000000Hz on i.MX6ULL only;
     * We need to set the max speed of ARM according to fuse map.
     */
    val >>= OCOTP_CFG3_SPEED_SHIFT;
    val &= 0x3;

    // 根据型号和grade, 关闭对应的时钟频率
    if (of_machine_is_compatible("fsl,imx6ul")) {
        if (val != OCOTP_CFG3_6UL_SPEED_696MHZ)
            if (dev_pm_opp_disable(dev, 696000000))
                dev_warn(dev, "failed to disable 696MHz OPP\n");
    }

    if (of_machine_is_compatible("fsl,imx6ull")) {
        if (val != OCOTP_CFG3_6ULL_SPEED_792MHZ)
            if (dev_pm_opp_disable(dev, 792000000))
                dev_warn(dev, "failed to disable 792MHz OPP\n");

        if (val != OCOTP_CFG3_6ULL_SPEED_900MHZ)
            if (dev_pm_opp_disable(dev, 900000000))
                dev_warn(dev, "failed to disable 900MHz OPP\n");
    }

    return ret;
}

freq_opp

//管理设备树中operating-points
drivers/opp/*

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