ARM PSCI在ATF和Linux kernel中的实现

Linux内核中cpu_ops的实现因架构而已，对于ARM64架构一般通过执行smc指令进入EL3异常，由ATF执行PSCI功能。然后将结果返回给Linux。

这中间涉及到【Linux kernel的cpu_ops、psci_ops】、【SMC/HVC】、【PSCI】、【ATF的PSCI】相关等等。

1. PSCI规格

目前PSCI最新规格为v1.1，这里以v1.0为参考：《POWER STATE COORDINATION INTERFACE (PSCI) System Software on ARM® Systems》。

1.1 PSCI_VERSION

返回当前psci固件版本号。

1.2 CPU_SUSPEND

执行核的suspend操作，一般用于等待被唤醒后继续执行的子系统。

1.3 CPU_OFF

 用于hotplug中关闭调用此功能的核。被CPU_OFF关闭的仅能被CPU_ON打开。

1.4 CPU_ON

上电一个核，用于以下两种情况：

• 还未被启动的核
• 已经被CPU_OFF关闭的核。

1.5 AFFINITY_INFO

1.6 MIGRATE

可选。要求单核TOS将指向上下文迁移到一个指定核。

1.7 MIGRATE_INFO_TYPE

允许调用者查询当前TOS对多核支持情况。

1.8 MIGRATE_INFO_UP_CPU

可选。对单核TOS系统，此功能返回TOS当前驻存在哪个核上。

1.9 SYSTEM_OFF

1.10 SYSTEM_RESET

进行系统复位，没有入参也没有返回值。

1.11 PSCI_FEATURES

查询psci固件是否支持指定功能id及其特性。

1.12 CPU_FREEZE

1.13 CPU_DEFAULT_SUSPEND

1.14 NODE_HW_STATE

1.15 SYSTEM_SUSPEND

让系统进入深度低功耗模式。

1.16 SUSPEND_MODE

1.17 PSCI_STAT_RESIDENCY

1.18 PSCI_STAT_COUNT

2. ATF PSCI实现

参考：《《ARM Trusted Firmware》阅读笔记 PSCI》

3. Linux PSCI实现

PSCI主要负责CPU低功耗、热插拔功能，对接cpu_ops实现一系列函数。

在dt中配置psci属性，以及在

3.1 psci dts配置

 psci相关配置在dts中定义：

    psci {
        compatible = "arm,psci-0.2";
        method = "smc";
    };

说明使用的驱动是psci v0.2标准的接口。

3.2 psci驱动初始化

对psci初始化在setup_arch()中调用，psci_dt_init()从dt中解析出psci版本以及实现psci调用的方式(smc)。

void __init setup_arch(char **cmdline_p)
{
...
    if (acpi_disabled)
        psci_dt_init();
    else
        psci_acpi_init();
...
}


int __init psci_dt_init(void)
{
    struct device_node *np;
    const struct of_device_id *matched_np;
    psci_initcall_t init_fn;

    np = of_find_matching_node_and_match(NULL, psci_of_match, &matched_np);----进行dts设备匹配，这里对应psci-0.2。

    if (!np)
        return -ENODEV;

    init_fn = (psci_initcall_t)matched_np->data;-------------------------------对应的函数为psci_0_2_init()。
    return init_fn(np);
}

static const struct of_device_id psci_of_match[] __initconst = {
    { .compatible = "arm,psci",    .data = psci_0_1_init},
    { .compatible = "arm,psci-0.2",    .data = psci_0_2_init},
    { .compatible = "arm,psci-1.0",    .data = psci_0_2_init},
    {},
};

static int __init psci_0_2_init(struct device_node *np)
{
    int err;

    err = get_set_conduit_method(np);--------------------------------------从dt中解析出psci的method，这里为smc，表示psci功能通过smc(Secure Monitor Call：->EL3调用)实现。其他方式还有svc(Supervisor call：->EL1调用)和hvc(Hypervisor call：->EL2调用)。

    if (err)
        goto out_put_node;
    /*
     * Starting with v0.2, the PSCI specification introduced a call
     * (PSCI_VERSION) that allows probing the firmware version, so
     * that PSCI function IDs and version specific initialization
     * can be carried out according to the specific version reported
     * by firmware
     */
    err = psci_probe();

out_put_node:
    of_node_put(np);
    return err;
}

static int __init psci_probe(void)
{
    u32 ver = psci_get_version();--------------------------------------------------通过SMC的PSCI_0_2_FN_PSCI_VERSION功能id获取PSCI固件版本号。

    pr_info("PSCIv%d.%d detected in firmware.
",
            PSCI_VERSION_MAJOR(ver),
            PSCI_VERSION_MINOR(ver));

    if (PSCI_VERSION_MAJOR(ver) == 0 && PSCI_VERSION_MINOR(ver) < 2) {-------------驱动只支持psci 0.2及以上的psci固件。
        pr_err("Conflicting PSCI version detected.
");
        return -EINVAL;
    }

    psci_0_2_set_functions();------------------------------------------------------将linux中使用的psci_ops、arm_pm_off、pm_power_off对齐到具体PSCI的SMC功能id。

    psci_init_migrate();

    if (PSCI_VERSION_MAJOR(ver) >= 1) {--------------------------------------------对于>=v1.0版本psci，特殊处理suspend。
        psci_init_smccc();
        psci_init_cpu_suspend();
        psci_init_system_suspend();
    }

    return 0;
}

3.2.1 PSCI功能实现中转通道：SMC或HVC

kernel实现SMC调用的两种方式：SMC和HVC。get_set_conduit_method()的核心是根据dt中的method字段，选择合适的invoke_psci_fn函数。

enum psci_conduit {
    PSCI_CONDUIT_NONE,
    PSCI_CONDUIT_SMC,
    PSCI_CONDUIT_HVC,
};

static int get_set_conduit_method(struct device_node *np)
{
    const char *method;

    pr_info("probing for conduit method from DT.
");

    if (of_property_read_string(np, "method", &method)) {
        pr_warn("missing "method" property
");
        return -ENXIO;
    }

    if (!strcmp("hvc", method)) {
        set_conduit(PSCI_CONDUIT_HVC);
    } else if (!strcmp("smc", method)) {------------------------------根据dt中的method字段，设置invoke_psci_fn函数。
        set_conduit(PSCI_CONDUIT_SMC);
    } else {
        pr_warn("invalid "method" property: %s
", method);
        return -EINVAL;
    }
    return 0;
}

static void set_conduit(enum psci_conduit conduit)-----------------------HVC和SMC两种访问psci固件的方式，HVC表示当前OS为guest os；SMC表示从EL1直接访问EL3 psci固件。
{
    switch (conduit) {
    case PSCI_CONDUIT_HVC:
        invoke_psci_fn = __invoke_psci_fn_hvc;
        break;
    case PSCI_CONDUIT_SMC:
        invoke_psci_fn = __invoke_psci_fn_smc;
        break;
    default:
        WARN(1, "Unexpected PSCI conduit %d
", conduit);
    }

    psci_ops.conduit = conduit;
}

static unsigned long __invoke_psci_fn_hvc(unsigned long function_id,
            unsigned long arg0, unsigned long arg1,
            unsigned long arg2)
{
    struct arm_smccc_res res;

    arm_smccc_hvc(function_id, arg0, arg1, arg2, 0, 0, 0, 0, &res);
    return res.a0;
}

static unsigned long __invoke_psci_fn_smc(unsigned long function_id,
            unsigned long arg0, unsigned long arg1,
            unsigned long arg2)
{
    struct arm_smccc_res res;

    arm_smccc_smc(function_id, arg0, arg1, arg2, 0, 0, 0, 0, &res);
    return res.a0;
}


    .macro SMCCC instr
    .cfi_startproc
    instr    #0
    ldr    x4, [sp]
    stp    x0, x1, [x4, #ARM_SMCCC_RES_X0_OFFS]
    stp    x2, x3, [x4, #ARM_SMCCC_RES_X2_OFFS]
    ldr    x4, [sp, #8]
    cbz    x4, 1f /* no quirk structure */
    ldr    x9, [x4, #ARM_SMCCC_QUIRK_ID_OFFS]
    cmp    x9, #ARM_SMCCC_QUIRK_QCOM_A6
    b.ne    1f
    str    x6, [x4, ARM_SMCCC_QUIRK_STATE_OFFS]
1:    ret
    .cfi_endproc
    .endm

/*
 * void arm_smccc_smc(unsigned long a0, unsigned long a1, unsigned long a2,
 *          unsigned long a3, unsigned long a4, unsigned long a5,
 *          unsigned long a6, unsigned long a7, struct arm_smccc_res *res,
 *          struct arm_smccc_quirk *quirk)
 */
ENTRY(__arm_smccc_smc)
    SMCCC    smc
ENDPROC(__arm_smccc_smc)

/*
 * void arm_smccc_hvc(unsigned long a0, unsigned long a1, unsigned long a2,
 *          unsigned long a3, unsigned long a4, unsigned long a5,
 *          unsigned long a6, unsigned long a7, struct arm_smccc_res *res,
 *          struct arm_smccc_quirk *quirk)
 */
ENTRY(__arm_smccc_hvc)
    SMCCC    hvc
ENDPROC(__arm_smccc_hvc)

3.2.2 psci_ops函数集

struct psci_operations psci_ops是Linux下对应psci功能函数集，另外psci_function_id[]下标为LInux psci功能id，值为具体psci规格功能id，psci_function_id[]进行两者的转换。

struct psci_operations {
    u32 (*get_version)(void);------------------------------------------获取psci固件版本号。
    int (*cpu_suspend)(u32 state, unsigned long entry_point);----------
    int (*cpu_off)(u32 state);
    int (*cpu_on)(unsigned long cpuid, unsigned long entry_point);
    int (*migrate)(unsigned long cpuid);
    int (*affinity_info)(unsigned long target_affinity,
            unsigned long lowest_affinity_level);
    int (*migrate_info_type)(void);
    enum psci_conduit conduit;
    enum smccc_version smccc_version;
};

struct psci_operations psci_ops = {
    .conduit = PSCI_CONDUIT_NONE,
    .smccc_version = SMCCC_VERSION_1_0,
};

enum psci_function {
    PSCI_FN_CPU_SUSPEND,
    PSCI_FN_CPU_ON,
    PSCI_FN_CPU_OFF,
    PSCI_FN_MIGRATE,
    PSCI_FN_MAX,
};

static u32 psci_function_id[PSCI_FN_MAX];

psci_0_2_setfunction()主要设置了psci_ops函数集，以及arm_pm_restart和pm_power_off。

static void __init psci_0_2_set_functions(void)
{
    pr_info("Using standard PSCI v0.2 function IDs
");
    psci_ops.get_version = psci_get_version;

    psci_function_id[PSCI_FN_CPU_SUSPEND] =
                    PSCI_FN_NATIVE(0_2, CPU_SUSPEND);
    psci_ops.cpu_suspend = psci_cpu_suspend;

    psci_function_id[PSCI_FN_CPU_OFF] = PSCI_0_2_FN_CPU_OFF;
    psci_ops.cpu_off = psci_cpu_off;

    psci_function_id[PSCI_FN_CPU_ON] = PSCI_FN_NATIVE(0_2, CPU_ON);
    psci_ops.cpu_on = psci_cpu_on;

    psci_function_id[PSCI_FN_MIGRATE] = PSCI_FN_NATIVE(0_2, MIGRATE);
    psci_ops.migrate = psci_migrate;

    psci_ops.affinity_info = psci_affinity_info;

    psci_ops.migrate_info_type = psci_migrate_info_type;

    arm_pm_restart = psci_sys_reset;

    pm_power_off = psci_sys_poweroff;
}

对应psci的PSCI_VERSION功能，返回psci固件版本号。

通过PSCI_VERSION_MAJOR()和PSCI_VERSION_MINOR()解析。

static u32 psci_get_version(void)
{
    return invoke_psci_fn(PSCI_0_2_FN_PSCI_VERSION, 0, 0, 0);
}

对应psci的CPU_SUSPEND功能，state是将要进入的低功耗状态，entry_point是从低功耗状态返回后执行入口地址。

entry_point必须是物理地址或者虚拟机的IPA。

第三个参数是Powerdown功耗状态才会使用。

static int psci_cpu_suspend(u32 state, unsigned long entry_point)
{
    int err;
    u32 fn;

    fn = psci_function_id[PSCI_FN_CPU_SUSPEND];
    err = invoke_psci_fn(fn, state, entry_point, 0);
    return psci_to_linux_errno(err);
}

对应psci的CPU_OFF功能，让关闭调用此功能的核。

static int psci_cpu_off(u32 state)
{
    int err;
    u32 fn;

    fn = psci_function_id[PSCI_FN_CPU_OFF];
    err = invoke_psci_fn(fn, state, 0, 0);
    return psci_to_linux_errno(err);
}

对应psci的CPU_ON功能，给一个核上电。

cpuid为需要上电cpu的id；entry_point是CPU上电后运行入口物理地址或IPA，比如这里为secondary_entry()。如果第一次启动，可以传入context_id参数。

static int psci_cpu_on(unsigned long cpuid, unsigned long entry_point)
{
    int err;
    u32 fn;

    fn = psci_function_id[PSCI_FN_CPU_ON];
    err = invoke_psci_fn(fn, cpuid, entry_point, 0);
    return psci_to_linux_errno(err);
}


static int cpu_psci_cpu_boot(unsigned int cpu)
{
    int err = psci_ops.cpu_on(cpu_logical_map(cpu), __pa(secondary_entry));
    if (err)
        pr_err("failed to boot CPU%d (%d)
", cpu, err);

    return err;
}
    /*
     * Secondary entry point that jumps straight into the kernel. Only to
     * be used where CPUs are brought online dynamically by the kernel.
     */
ENTRY(secondary_entry)
    bl    el2_setup            // Drop to EL1
    bl    set_cpu_boot_mode_flag
    b    secondary_startup
ENDPROC(secondary_entry)

对应psci的MIGRATE功能，将TOS迁移到指定cpuid上执行。

cpuid将要迁移到cpu的id。

static int psci_migrate(unsigned long cpuid)
{
    int err;
    u32 fn;

    fn = psci_function_id[PSCI_FN_MIGRATE];
    err = invoke_psci_fn(fn, cpuid, 0, 0);
    return psci_to_linux_errno(err);
}

对应psci的AFFINITY_INFO功能，

static int psci_affinity_info(unsigned long target_affinity,
        unsigned long lowest_affinity_level)
{
    return invoke_psci_fn(PSCI_FN_NATIVE(0_2, AFFINITY_INFO),
                  target_affinity, lowest_affinity_level, 0);
}

对应psci的MIGRATE_INFO_TYPE功能，获取TOS在多核环境下迁移能力。

0 - TOS运行在一个核上，但是可以迁移到任何违背CPU_OFF的核。

1 - TOS仅运行在一个核上，不支持MIGRATE功能。

2 - TOS不存在或者不需要MIGRATE功能。

NOT_SUPPORTED - 不需要MIGRATE。

static int psci_migrate_info_type(void)
{
    return invoke_psci_fn(PSCI_0_2_FN_MIGRATE_INFO_TYPE, 0, 0, 0);
}

/* PSCI v0.2 multicore support in Trusted OS returned by MIGRATE_INFO_TYPE */
#define PSCI_0_2_TOS_UP_MIGRATE            0
#define PSCI_0_2_TOS_UP_NO_MIGRATE        1
#define PSCI_0_2_TOS_MP                2

对应psci的SYSTEM_RESET功能，执行系统复位功能。

static void psci_sys_reset(enum reboot_mode reboot_mode, const char *cmd)
{
    invoke_psci_fn(PSCI_0_2_FN_SYSTEM_RESET, 0, 0, 0);
}


/*
 * Restart requires that the secondary CPUs stop performing any activity
 * while the primary CPU resets the system. Systems with multiple CPUs must
 * provide a HW restart implementation, to ensure that all CPUs reset at once.
 * This is required so that any code running after reset on the primary CPU
 * doesn't have to co-ordinate with other CPUs to ensure they aren't still
 * executing pre-reset code, and using RAM that the primary CPU's code wishes
 * to use. Implementing such co-ordination would be essentially impossible.
 */
void machine_restart(char *cmd)
{
...
    /* Now call the architecture specific reboot code. */
    if (arm_pm_restart)
        arm_pm_restart(reboot_mode, cmd);------------------调用psci_sys_reset()函数。
    else
        do_kernel_restart(cmd);

    /*
     * Whoops - the architecture was unable to reboot.
     */
    printk("Reboot failed -- System halted
");
    while (1);
}

对应psci的SYSTEM_OFF功能， 关闭系统。无入参和返回值。

static void psci_sys_poweroff(void)
{
    invoke_psci_fn(PSCI_0_2_FN_SYSTEM_OFF, 0, 0, 0);
}

/*
 * Power-off simply requires that the secondary CPUs stop performing any
 * activity (executing tasks, handling interrupts). smp_send_stop()
 * achieves this. When the system power is turned off, it will take all CPUs
 * with it.
 */
void machine_power_off(void)
{
    local_irq_disable();
    smp_send_stop();
    if (pm_power_off)
        pm_power_off();---------------------------调用psci_sys_poweroff()。
}

3.3 TOS驻存CPU不允许hotplug

psci_init_migrate()获取当前TOS驻存的CPU id，并赋值给resident_cpu。

/*
 * Detect the presence of a resident Trusted OS which may cause CPU_OFF to
 * return DENIED (which would be fatal).
 */
static void __init psci_init_migrate(void)
{
    unsigned long cpuid;
    int type, cpu = -1;

    type = psci_ops.migrate_info_type();-----------------------------------------获取psci支持的TOS服务迁移类型。

    if (type == PSCI_0_2_TOS_MP) {
        pr_info("Trusted OS migration not required
");
        return;
    }

    if (type == PSCI_RET_NOT_SUPPORTED) {
        pr_info("MIGRATE_INFO_TYPE not supported.
");
        return;
    }

    if (type != PSCI_0_2_TOS_UP_MIGRATE &&
        type != PSCI_0_2_TOS_UP_NO_MIGRATE) {
        pr_err("MIGRATE_INFO_TYPE returned unknown type (%d)
", type);
        return;
    }

    cpuid = psci_migrate_info_up_cpu();------------------------------------------MIGRATE_INFO_UP_CPU获取TOS驻存CPU的mpidr值。
    if (cpuid & ~MPIDR_HWID_BITMASK) {
        pr_warn("MIGRATE_INFO_UP_CPU reported invalid physical ID (0x%lx)
",
            cpuid);
        return;
    }

    cpu = get_logical_index(cpuid);----------------------------------------------将mpidr值转换成cpu逻辑id，并赋值给resident_cpu。
    resident_cpu = cpu >= 0 ? cpu : -1;

    pr_info("Trusted OS resident on physical CPU 0x%lx
", cpuid);
}

当需要CPU进行hotplug之前，调用cpu_disable来检查CPU是否支持hotplug。如果需要进行hotplug的cpu是resident_cpu，则返回EPERM错误。

bool psci_tos_resident_on(int cpu)
{
    return cpu == resident_cpu;
}
static int cpu_psci_cpu_disable(unsigned int cpu)
{
    /* Fail early if we don't have CPU_OFF support */
    if (!psci_ops.cpu_off)
        return -EOPNOTSUPP;

    /* Trusted OS will deny CPU_OFF */
    if (psci_tos_resident_on(cpu))
        return -EPERM;

    return 0;
}

const struct cpu_operations cpu_psci_ops = {
    .name        = "psci",
...
#ifdef CONFIG_HOTPLUG_CPU
    .cpu_disable    = cpu_psci_cpu_disable,
    .cpu_die    = cpu_psci_cpu_die,
    .cpu_kill    = cpu_psci_cpu_kill,
#endif
};

3.4 v1.0及以上suspend处理

static void __init psci_init_cpu_suspend(void)
{
    int feature = psci_features(psci_function_id[PSCI_FN_CPU_SUSPEND]);

    if (feature != PSCI_RET_NOT_SUPPORTED)
        psci_cpu_suspend_feature = feature;
}

static void __init psci_init_system_suspend(void)
{
    int ret;

    if (!IS_ENABLED(CONFIG_SUSPEND))
        return;

    ret = psci_features(PSCI_FN_NATIVE(1_0, SYSTEM_SUSPEND));

    if (ret != PSCI_RET_NOT_SUPPORTED)
        suspend_set_ops(&psci_suspend_ops);
}

static const struct platform_suspend_ops psci_suspend_ops = {
    .valid          = suspend_valid_only_mem,
    .enter          = psci_system_suspend_enter,
};

static int psci_system_suspend_enter(suspend_state_t state)
{
    return cpu_suspend(0, psci_system_suspend);
}

 对应psci的SYSTEM_SUSPEND功能，实现suspend到ram功能，类似于进入最深度低功耗的CPU_SUSPEND。

成功则没有返回值，失败则返回NOT_SUPPORTED、INVALID_ADDRESS、ALREADY_ON之一。

static int psci_system_suspend(unsigned long unused)
{
    return invoke_psci_fn(PSCI_FN_NATIVE(1_0, SYSTEM_SUSPEND),
                  virt_to_phys(cpu_resume), 0, 0);
}

4. cpu_ops到psci固件通路

大致调用路径：cpu_ops->cpu_psci_ops->psci_ops->invoke_psci_fn()->SMCC。

dt中低功耗配置：

    cpus {
        #address-cells = <0x2>;
        #size-cells = <0x0>;

        cpu@0 {
            compatible = "arm,cortex-a53";
            device_type = "cpu";
            reg = <0x0 0x0>;
            enable-method = "psci";
            clock-latency = <0x186a0>;
            cpu-idle-states = <0xc 0xd>;
        };

        cpu@1 {
...
        };
...
    };

setup_arch()中调用cpu_read_bootcpu_ops()，经过一系列判断cpu_ops[0]指向cpu_psci_ops。cpu_psci_ops中大部分实现通过调用psci_ops，在函数psci_0_2_set_functions()中指定了psci_ops函数集，基本通过invoke_psci_fn()发送SMC调用由psci固件在EL3执行。

void __init setup_arch(char **cmdline_p)
{
...
    if (acpi_disabled)
        psci_dt_init();
    else
        psci_acpi_init();

    cpu_read_bootcpu_ops();
...
}

static inline void __init cpu_read_bootcpu_ops(void)
{
    cpu_read_ops(0);
}

int __init cpu_read_ops(int cpu)
{
    const char *enable_method = cpu_read_enable_method(cpu);------------------------读取当前cpu在dt中的enable-method配置，这里以psci为例。

    if (!enable_method)
        return -ENODEV;

    cpu_ops[cpu] = cpu_get_ops(enable_method);
    if (!cpu_ops[cpu]) {
        pr_warn("Unsupported enable-method: %s
", enable_method);
        return -EOPNOTSUPP;
    }

    return 0;
}

static const struct cpu_operations * __init cpu_get_ops(const char *name)
{
    const struct cpu_operations **ops;

    ops = acpi_disabled ? dt_supported_cpu_ops : acpi_supported_cpu_ops;

    while (*ops) {
        if (!strcmp(name, (*ops)->name))-----------------------------------------------在关闭acpi情况下，根据从dt中读取的字符串匹配到cpu_psci_ops函数集。
            return *ops;

        ops++;
    }

    return NULL;
}

static const struct cpu_operations *dt_supported_cpu_ops[] __initconst = {
    &smp_spin_table_ops,
    &cpu_psci_ops,
    NULL,
};

const struct cpu_operations cpu_psci_ops = {
    .name        = "psci",
#ifdef CONFIG_CPU_IDLE
    .cpu_init_idle    = psci_cpu_init_idle,
    .cpu_suspend    = psci_cpu_suspend_enter,
#endif
    .cpu_init    = cpu_psci_cpu_init,
    .cpu_prepare    = cpu_psci_cpu_prepare,
    .cpu_boot    = cpu_psci_cpu_boot,
#ifdef CONFIG_HOTPLUG_CPU
    .cpu_disable    = cpu_psci_cpu_disable,
    .cpu_die    = cpu_psci_cpu_die,
    .cpu_kill    = cpu_psci_cpu_kill,
#endif
};