轉自：https://www.cnblogs.com/arnoldlu/p/14211367.html
Linux內核中cpu_ops的實現因架構而已，對於ARM64架構一般通過執行smc指令進入EL3異常，由ATF執行PSCI功能。然後將結果返回給Linux。
這中間涉及到【Linux kernel的cpu_ops、psci_ops】、【SMC/HVC】、【PSCI】、【ATF的PSCI】相關等等。
1. PSCI規格
目前PSCI最新規格爲v1.1，這裏以v1.0爲參考：《POWER STATE COORDINATION INTERFACE (PSCI) System Software on ARM® Systems》。
1.1 PSCI_VERSION
返回當前psci固件版本號。
1.2 CPU_SUSPEND
執行核的suspend操作，一般用於等待被喚醒後繼續執行的子系統。
1.3 CPU_OFF
用於hotplug中關閉調用此功能的核。被CPU_OFF關閉的僅能被CPU_ON打開。
1.4 CPU_ON
上電一個核，用於以下兩種情況：
- 還未被啓動的核
- 已經被CPU_OFF關閉的核。
1.5 AFFINITY_INFO
1.6 MIGRATE
可選。要求單核TOS將指向上下文遷移到一個指定核。
1.7 MIGRATE_INFO_TYPE
允許調用者查詢當前TOS對多核支持情況。
1.8 MIGRATE_INFO_UP_CPU
可選。對單核TOS系統，此功能返回TOS當前駐存在哪個核上。
1.9 SYSTEM_OFF
1.10 SYSTEM_RESET
進行系統復位，沒有入參也沒有返回值。
1.11 PSCI_FEATURES
查詢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
讓系統進入深度低功耗模式。
1.16 SUSPEND_MODE
1.17 PSCI_STAT_RESIDENCY
1.18 PSCI_STAT_COUNT
2. ATF PSCI實現
參考：《《ARM Trusted Firmware》閱讀筆記 PSCI》
3. Linux PSCI實現
PSCI主要負責CPU低功耗、熱插拔功能，對接cpu_ops實現一系列函數。
在dt中配置psci屬性，以及在
3.1 psci dts配置
psci相關配置在dts中定義：
psci {
compatible = "arm,psci-0.2";
method = "smc";
};
說明使用的驅動是psci v0.2標準的接口。
3.2 psci驅動初始化
對psci初始化在setup_arch()中調用，psci_dt_init()從dt中解析出psci版本以及實現psci調用的方式(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);----進行dts設備匹配，這裏對應psci-0.2。 if (!np) return -ENODEV; init_fn = (psci_initcall_t)matched_np->data;-------------------------------對應的函數爲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);--------------------------------------從dt中解析出psci的method，這裏爲smc，表示psci功能通過smc(Secure Monitor Call：->EL3調用)實現。其他方式還有svc(Supervisor call：->EL1調用)和hvc(Hypervisor call：->EL2調用)。 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();--------------------------------------------------通過SMC的PSCI_0_2_FN_PSCI_VERSION功能id獲取PSCI固件版本號。 pr_info("PSCIv%d.%d detected in firmware.\n", PSCI_VERSION_MAJOR(ver), PSCI_VERSION_MINOR(ver)); if (PSCI_VERSION_MAJOR(ver) == 0 && PSCI_VERSION_MINOR(ver) < 2) {-------------驅動只支持psci 0.2及以上的psci固件。 pr_err("Conflicting PSCI version detected.\n"); return -EINVAL; } psci_0_2_set_functions();------------------------------------------------------將linux中使用的psci_ops、arm_pm_off、pm_power_off對齊到具體PSCI的SMC功能id。 psci_init_migrate(); if (PSCI_VERSION_MAJOR(ver) >= 1) {--------------------------------------------對於>=v1.0版本psci，特殊處理suspend。 psci_init_smccc(); psci_init_cpu_suspend(); psci_init_system_suspend(); } return 0; }
3.2.1 PSCI功能實現中轉通道：SMC或HVC
kernel實現SMC調用的兩種方式：SMC和HVC。get_set_conduit_method()的核心是根據dt中的method字段，選擇合適的invoke_psci_fn函數。
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.\n");
if (of_property_read_string(np, "method", &method)) {
pr_warn("missing \"method\" property\n");
return -ENXIO;
}
if (!strcmp("hvc", method)) {
set_conduit(PSCI_CONDUIT_HVC);
} else if (!strcmp("smc", method)) {------------------------------根據dt中的method字段，設置invoke_psci_fn函數。
set_conduit(PSCI_CONDUIT_SMC);
} else {
pr_warn("invalid \"method\" property: %s\n", method);
return -EINVAL;
}
return 0;
}
static void set_conduit(enum psci_conduit conduit)-----------------------HVC和SMC兩種訪問psci固件的方式，HVC表示當前OS爲guest os；SMC表示從EL1直接訪問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\n", 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函數集
struct psci_operations psci_ops是Linux下對應psci功能函數集，另外psci_function_id[]下標爲LInux psci功能id，值爲具體psci規格功能id，psci_function_id[]進行兩者的轉換。
struct psci_operations {
u32 (*get_version)(void);------------------------------------------獲取psci固件版本號。
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()主要設置了psci_ops函數集，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\n"); 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; }
對應psci的PSCI_VERSION功能，返回psci固件版本號。
通過PSCI_VERSION_MAJOR()和PSCI_VERSION_MINOR()解析。
對應psci的CPU_SUSPEND功能，state是將要進入的低功耗狀態，entry_point是從低功耗狀態返回後執行入口地址。
entry_point必須是物理地址或者虛擬機的IPA。
第三個參數是Powerdown功耗狀態纔會使用。
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); }
對應psci的CPU_OFF功能，讓關閉調用此功能的核。
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); }
對應psci的CPU_ON功能，給一個核上電。
cpuid爲需要上電cpu的id；entry_point是CPU上電後運行入口物理地址或IPA，比如這裏爲secondary_entry()。如果第一次啓動，可以傳入context_id參數。
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)\n", 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)
對應psci的MIGRATE功能，將TOS遷移到指定cpuid上執行。
cpuid將要遷移到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); }
對應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); }
對應psci的MIGRATE_INFO_TYPE功能，獲取TOS在多核環境下遷移能力。
0 - TOS運行在一個核上，但是可以遷移到任何違背CPU_OFF的核。
1 - TOS僅運行在一個核上，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
對應psci的SYSTEM_RESET功能，執行系統復位功能。
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);------------------調用psci_sys_reset()函數。 else do_kernel_restart(cmd); /* * Whoops - the architecture was unable to reboot. */ printk("Reboot failed -- System halted\n"); while (1); }
對應psci的SYSTEM_OFF功能， 關閉系統。無入參和返回值。
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();---------------------------調用psci_sys_poweroff()。 }
3.3 TOS駐存CPU不允許hotplug
psci_init_migrate()獲取當前TOS駐存的CPU id，並賦值給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();-----------------------------------------獲取psci支持的TOS服務遷移類型。 if (type == PSCI_0_2_TOS_MP) { pr_info("Trusted OS migration not required\n"); return; } if (type == PSCI_RET_NOT_SUPPORTED) { pr_info("MIGRATE_INFO_TYPE not supported.\n"); 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)\n", type); return; } cpuid = psci_migrate_info_up_cpu();------------------------------------------MIGRATE_INFO_UP_CPU獲取TOS駐存CPU的mpidr值。 if (cpuid & ~MPIDR_HWID_BITMASK) { pr_warn("MIGRATE_INFO_UP_CPU reported invalid physical ID (0x%lx)\n", cpuid); return; } cpu = get_logical_index(cpuid);----------------------------------------------將mpidr值轉換成cpu邏輯id，並賦值給resident_cpu。 resident_cpu = cpu >= 0 ? cpu : -1; pr_info("Trusted OS resident on physical CPU 0x%lx\n", cpuid); }
當需要CPU進行hotplug之前，調用cpu_disable來檢查CPU是否支持hotplug。如果需要進行hotplug的cpu是resident_cpu，則返回EPERM錯誤。
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處理
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); }
對應psci的SYSTEM_SUSPEND功能，實現suspend到ram功能，類似於進入最深度低功耗的CPU_SUSPEND。
成功則沒有返回值，失敗則返回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
大致調用路徑：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()中調用cpu_read_bootcpu_ops()，經過一系列判斷cpu_ops[0]指向cpu_psci_ops。cpu_psci_ops中大部分實現通過調用psci_ops，在函數psci_0_2_set_functions()中指定了psci_ops函數集，基本通過invoke_psci_fn()發送SMC調用由psci固件在EL3執行。
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);------------------------讀取當前cpu在dt中的enable-method配置，這裏以psci爲例。
if (!enable_method)
return -ENODEV;
cpu_ops[cpu] = cpu_get_ops(enable_method);
if (!cpu_ops[cpu]) {
pr_warn("Unsupported enable-method: %s\n", 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))-----------------------------------------------在關閉acpi情況下，根據從dt中讀取的字符串匹配到cpu_psci_ops函數集。
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
};
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