linux休眠唤醒（四）
2016-09-24 21:32
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转自http://blog.csdn.net/dwyane_zhang/article/details/7099725
suspend第三、四、五阶段：platform、processor、core
static int suspend_enter(suspend_state_t state)
{
int error;
if (suspend_ops->prepare) {
// 平台特定的函数，mtkpm.c, 有定义，对pmic和cpu dll的一些设置
error = suspend_ops->prepare();
if (error)
return error;
}
error = dpm_suspend_noirq(PMSG_SUSPEND);
// 对于一些non-sysdev devices，需要调用禁止中断的dpm_suspend函数来suspend那些设备
if (error) {
printk(KERN_ERR "PM: Some devices failed to power down/n");
goto Platfrom_finish;
}
if (suspend_ops->prepare_late) { // 这里没定义
error = suspend_ops->prepare_late();
if (error)
goto Power_up_devices;
}
if (suspend_test(TEST_PLATFORM)) // suspend第3阶段到此为止
goto Platform_wake;
error = disable_nonboot_cpus(); // disable nonboot cpus
if (error || suspend_test(TEST_CPUS)) // suspend第4阶段到此为止
goto Enable_cpus;
arch_suspend_disable_irqs(); // 中断禁止
BUG_ON(!irqs_disabled());
error = sysdev_suspend(PMSG_SUSPEND); // kernel/driver/base/sys.c
// suspend system devices
if (!error) {
if (!suspend_test(TEST_CORE)) // suspend第5阶段到此为止
error = suspend_ops->enter(state);
// 真正才进入suspend，调用的函数时平台特定的suspend enter函数， // mtkpm.c, 在下面列出mtk平台的该函数实现，供分析：
// 如果有唤醒源被操作，那么处理将会被wakeup，先做一些平台相 // 关的动作，最后从函数suspend_ops->enter()中返回，这之后的唤 // 醒操作实际上是按照suspend流程的相反顺序的来走的。
sysdev_resume(); // resuem system devices
// 跳到本文档最后面，将会有一个总结，这里会展示出正常的suspend和resume的时候函数调用
}
arch_suspend_enable_irqs();
BUG_ON(irqs_disabled());
Enable_cpus:
enable_nonboot_cpus();
Platform_wake:
if (suspend_ops->wake) // 平台无定义
suspend_ops->wake();
Power_up_devices:
dpm_resume_noirq(PMSG_RESUME);
Platfrom_finish:
if (suspend_ops->finish) // 做和函数suspend_ops->prepare()相反的工作
suspend_ops->finish();
return error;
}
static int mtk_pm_enter(suspend_state_t state)
{
_Chip_pm_enter(state);
return 0;
}
int _Chip_pm_enter(suspend_state_t state)
{
MSG_FUNC_ENTRY();
printk("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@/n");
printk("_Chip_pm_enter @@@@@@@@@@@@@@@@@@@@@@/n");
printk(" @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@/n");
/* ensure the debug is initialised (if enabled) */
switch (state)
{
case PM_SUSPEND_ON:
MSG(SUSP,"mt6516_pm_enter PM_SUSPEND_ON/n/r");
break;
case PM_SUSPEND_STANDBY:
MSG(SUSP,"mt6516_pm_enter PM_SUSPEND_STANDBY/n/r");
break;
case PM_SUSPEND_MEM: // 只支持mem的系统省电模式
MSG(SUSP,"mt6516_pm_enter PM_SUSPEND_MEM/n/r");
if (g_ChipVer == CHIP_VER_ECO_2)
mt6516_pm_SuspendEnter();
// 让cpu进入省电模式的函数，真正休眠之后，执行的代码会停在这个函数中，直到外部有EINT将其cpu唤醒，停下来的代码才继续执行，也就是正常按下了唤醒键的时候。
break;
case PM_SUSPEND_MAX:
MSG(SUSP,"mt6516_pm_enter PM_SUSPEND_MAX/n/r");
MSG(SUSP,"Not support for MT6516/n/r");
break;
default:
MSG(SUSP,"mt6516_pm_enter Error state/n/r");
break;
}
return 0;
}
void mt6516_pm_SuspendEnter(void)
{
UINT32 u32TCM = 0xF0400000;
UINT32 u4SuspendAddr = 0;
UINT32 u4Status, u4BATVol;
UINT32 counter = 0;
/* Check Chip Version*/
if (g_ChipVer == CHIP_VER_ECO_1)
u4SuspendAddr = u32TCM;
else if(g_ChipVer == CHIP_VER_ECO_2)
u4SuspendAddr = __virt_to_phys((unsigned long)MT6516_CPUSuspend);
/*wifi low power optimization : shutdown MCPLL & VSDIO */
wifi_lowpower_opt(TRUE);
/* Check PM related register*/
mt6516_pm_RegDump();
//mt6326_check_power();
DRV_WriteReg32(APMCUSYS_PDN_SET0,0x04200000);
/* STEP7: Set AP_SM_CNF(DxF003C22C) to wanted wake-up source. 设置唤醒源*/
#if defined(PLATFORM_EVB)
mt6516_pm_SetWakeSrc((1<< WS_KP)|(1<<WS_EINT)|(1<<WS_RTC));
#elif defined(PMIC_BL_SETTING)
mt6516_pm_SetWakeSrc((1<<
WS_KP)|(1<<WS_EINT)|(1<<WS_CCIF)|(1<<WS_SM)|(1<<WS_RTC));
#else
mt6516_pm_SetWakeSrc((1<<WS_EINT)|(1<<WS_CCIF)|(1<<WS_SM)|(1<<WS_RTC));
//mt6516_pm_SetWakeSrc((1<<WS_SM));
#endif
/* Save interrupt masks*/
irqMask_L = *MT6516_IRQ_MASKL;
irqMask_H = *MT6516_IRQ_MASKH;
mt6516_pm_Maskinterrupt(); // 20100316 James
while(1)
{
#ifdef AP_MD_EINT_SHARE_DATA
/* Update Sleep flag*/
mt6516_EINT_SetMDShareInfo();
mt6516_pm_SleepWorkAround();
#endif
/* Enter suspend mode, mt6516_slpctrl.s */
if ( g_Sleep_lock <= 0 )
u4Status = MT6516_CPUSuspend (u4SuspendAddr, u32TCM);
else
MSG(SUSP,"Someone lock sleep/n/r");
#ifdef AP_MD_EINT_SHARE_DATA
mt6516_pm_SleepWorkAroundUp();
#endif
/* Check Sleep status*/
u4Status = mt6516_pm_CheckStatus();
if (u4Status == RET_WAKE_TIMEOUT)
{
#ifndef PLATFORM_EVB
DRV_WriteReg32(APMCUSYS_PDN_CLR0,0x04200000);
u4BATVol = (mt6516_pm_GetOneChannelValue(VBAT_CHANNEL,VBAT_COUNT)/VBAT_COUNT);
DRV_WriteReg32(APMCUSYS_PDN_SET0,0x04200000);
MSG(SUSP,"counter = %d, vbat = %d/n/r",counter++, u4BATVol);
if(u4BATVol <= LOW_BAT_ALARM)
{
MSG(SUSP,"Battery Low!!Power off/n/r");
bBAT_UVLO = TRUE;
goto SLP_EXIT;
}
#endif
}
else
{
MSG(SUSP,"leave sleep, wakeup!!/n/r");
goto SLP_EXIT;
//break;
}
}
SLP_EXIT:
wifi_lowpower_opt(FALSE);
/* Restore interrupt mask ; */
*MT6516_IRQ_MASKL = irqMask_L;
*MT6516_IRQ_MASKH = irqMask_H;
}
函数MT6516_CPUSuspend (u4SuspendAddr, u32TCM)是一段汇编代码，在文件：
Kernel/arch/arm/amch-mt6516/mt6516_slpctrl.S中。下面是这段汇编代码片段，看一看也蛮有意思，因为处理进入low power模式之后，是停留在该函数之中的。
ENTRY(MT6516_CPUSuspend)
stmfd sp!, {r4-r12, lr}
// r0 = MT6516_CPUSuspend physical address,
// r1 = TCM address
mov r4, r0
mov r9, r1
// Set SVC mode
mrs r0, cpsr
bic r0, r0, #MODE_MASK1
orr r1, r0, #Mode_SVC
// Set I/F bit, disable IRQ and FIQ
orr r1, r1, #I_Bit|F_Bit
// Update CPSR
msr cpsr_cxsf, r1
// calculate the physical address of instruction after disable MMU
ldr r0, =PhysicalPart
ldr r1, =MT6516_CPUSuspend
sub r0, r0, r1
mov r1, r4
// Now r0 is the physical address of PhysicalPart
add r0, r0, r1
...
...
// Power down Cache and MMU, MCU_MEM_PDN
ldr r0, =0xF0001308
ldr r1, [r0]
// ldr r1, =0xFFFFFFFF
orr r1, r1, #0x0F
str r1, [r0]
// STEP1: Set AP SLEEP (IRQ CODE: 0x36) to level sensitive on CIRQ.
// already done when system start.
// STEP2: Unmask AP SLEEP CTRL interrupt.
// already done at mt6516_pm_Maskinterrupt.
// STEP3: EOI AP SLEEP interrupt.
// already done at mt6516_pm_Maskinterrupt.
// STEP4: Read clear AP_SM_STA (OxF003C21C).
// already done at mt6516_pm_Maskinterrupt.
// STEP5: Set AP_SM_PAUSE_M(0x8003C200) and AP_SM_PAUSE_L(0x8003C204) for sleep duration. 16 seconds as default
...
// STEP6: Set AP_SM_CLK_SETTLE(0xF003C208) to 0x64. Must over 5ms
...
// STEP7: Set AP_SM_CNF(DxF003C22C) to wanted wake-up source. (TP, GPT, MSDC, RTC, EINT, KP or SM)
// already done at mt6516_pm_SuspendEnter
// STEP8: Set AP_SM_CON[1]:PAUSE_START to 1 to enable AP sleep controller.
...
// STEP9: Execute the CP15 command(MCR p15, 0, r0, c7, c0, 4),
// then ARM9 MCU enters low power state
// and STANDBYWFI signal becomes HIGH. CLOCK_OFF signal is issued to Clock Management Unit,
// and then AP MCU Sub-system clock is gated and VCXO OFF signal is issued to AP Sleep Controller.
mov r0, #0
mcr p15, 0, r0,c7,c0,4
// wait till interrupt occurs
// polling AP_SM_STA
mov r2, #0
mov r3, #0x10
15:
//mov r10, r1
// Power up I-Cache
...
//delay
...
// Power up I-Cache upper 16KB
...
//delay
...
// Power up D-Cache
...
//delay
...
// Power up D-Cache upper 16KB
...
//delay
...
// Clean and invalid DCache
// Invalidate instruction cache
// TCM_START_UA saved in r9
mov r2, r9
add r1, r1, r2
// make sure no stall on ¨mov pc,r0〃 below
cmp r1, #0
// restore MMU
mov r4, #0
// access domain 0
// TTB
// flush TLBs
// Turn on MMU
//test
mcr p15, 0, r6, c1, c0, 0
//mov pc, r1
nop
nop
VirtualPart:
nop
nop
mov r0, r10
ldmia sp!, {r4-r12, lr}
mov pc, lr
Nop
六、系统正常suspend和resume时函数调用和配对
enter_state(state)
--> sys_sync()
--> suspend_prepare()
--> pm_prepare_console()
--> pm_notifier_call_chain(PM_SUSPEND_PREPARE)
--> usermodehelper_disable()
--> suspend_freeze_processes()
--> suspend_devices_and_enter(state)
--> suspend_ops->begin(state)
--> _Chip_pm_begin()
--> suspend_console() // 此后串口无信息出来，缓存起来等后面resume打出
--> dpm_suspend_start(PMSG_SUSPEND)
--> dpm_prepare(state)
--> device_prepare(dev, state)
--> dpm_suspend(state)
--> device_suspend(dev, state)
--> suspend_enter(state)
--> suspend_ops->prepare()
--> _Chip_pm_prepare()
--> SetARM9Freq(DIV_4_104)
--> dpm_suspend_noirq(PMSG_SUSPEND)
--> suspend_ops->prepare_late() // 无定义
--> disable_nonboot_cpus()
--> arch_suspend_disable_irqs()
--> sysdev_suspend(PMSG_SUSPEND)
--> suspend_ops->enter(state)
--> _Chip_pm_enter(state)
--> mt6516_pm_SuspendEnter()
--> MT6516_CPUSuspend() // 汇编函数，suspend cpu
<-- MT6516_CPUSuspend() // 汇编函数，resume cpu
<-- mt6516_pm_CheckStatus()
<-- return 0
<-- return 0
<-- sysdev_resume()
<-- arch_suspend_enable_irqs()
<-- enable_nonboot_cpus()
<-- suspend_ops->wake() // 无定义
<-- dpm_resume_noirq(PMSG_RESUME)
<-- suspend_ops->finish()
<-- _Chip_pm_finish()
<-- SetARM9Freq(DIV_1_416)
<-- return 0
<-- return 0
<-- dpm_resume_end(PMSG_RESUME)
<-- dpm_resume(state)
<-- device_resume(dev, state)
<-- dpm_complete(state)
<-- device_complete(dev, state)
<-- resume_console() // 打印出缓存中的信息
<-- suspend_ops->end()
<-- return 0
<-- suspend_finish()
<-- suspend_thaw_processes()
<-- usermodehelper_enable()
<-- pm_notifier_call_chain(PM_POST_SUSPEND)
<-- pm_restore_console()
<-- return 0
suspend第三、四、五阶段：platform、processor、core
static int suspend_enter(suspend_state_t state)
{
int error;
if (suspend_ops->prepare) {
// 平台特定的函数，mtkpm.c, 有定义，对pmic和cpu dll的一些设置
error = suspend_ops->prepare();
if (error)
return error;
}
error = dpm_suspend_noirq(PMSG_SUSPEND);
// 对于一些non-sysdev devices，需要调用禁止中断的dpm_suspend函数来suspend那些设备
if (error) {
printk(KERN_ERR "PM: Some devices failed to power down/n");
goto Platfrom_finish;
}
if (suspend_ops->prepare_late) { // 这里没定义
error = suspend_ops->prepare_late();
if (error)
goto Power_up_devices;
}
if (suspend_test(TEST_PLATFORM)) // suspend第3阶段到此为止
goto Platform_wake;
error = disable_nonboot_cpus(); // disable nonboot cpus
if (error || suspend_test(TEST_CPUS)) // suspend第4阶段到此为止
goto Enable_cpus;
arch_suspend_disable_irqs(); // 中断禁止
BUG_ON(!irqs_disabled());
error = sysdev_suspend(PMSG_SUSPEND); // kernel/driver/base/sys.c
// suspend system devices
if (!error) {
if (!suspend_test(TEST_CORE)) // suspend第5阶段到此为止
error = suspend_ops->enter(state);
// 真正才进入suspend，调用的函数时平台特定的suspend enter函数， // mtkpm.c, 在下面列出mtk平台的该函数实现，供分析：
// 如果有唤醒源被操作，那么处理将会被wakeup，先做一些平台相 // 关的动作，最后从函数suspend_ops->enter()中返回，这之后的唤 // 醒操作实际上是按照suspend流程的相反顺序的来走的。
sysdev_resume(); // resuem system devices
// 跳到本文档最后面，将会有一个总结，这里会展示出正常的suspend和resume的时候函数调用
}
arch_suspend_enable_irqs();
BUG_ON(irqs_disabled());
Enable_cpus:
enable_nonboot_cpus();
Platform_wake:
if (suspend_ops->wake) // 平台无定义
suspend_ops->wake();
Power_up_devices:
dpm_resume_noirq(PMSG_RESUME);
Platfrom_finish:
if (suspend_ops->finish) // 做和函数suspend_ops->prepare()相反的工作
suspend_ops->finish();
return error;
}
static int mtk_pm_enter(suspend_state_t state)
{
_Chip_pm_enter(state);
return 0;
}
int _Chip_pm_enter(suspend_state_t state)
{
MSG_FUNC_ENTRY();
printk("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@/n");
printk("_Chip_pm_enter @@@@@@@@@@@@@@@@@@@@@@/n");
printk(" @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@/n");
/* ensure the debug is initialised (if enabled) */
switch (state)
{
case PM_SUSPEND_ON:
MSG(SUSP,"mt6516_pm_enter PM_SUSPEND_ON/n/r");
break;
case PM_SUSPEND_STANDBY:
MSG(SUSP,"mt6516_pm_enter PM_SUSPEND_STANDBY/n/r");
break;
case PM_SUSPEND_MEM: // 只支持mem的系统省电模式
MSG(SUSP,"mt6516_pm_enter PM_SUSPEND_MEM/n/r");
if (g_ChipVer == CHIP_VER_ECO_2)
mt6516_pm_SuspendEnter();
// 让cpu进入省电模式的函数，真正休眠之后，执行的代码会停在这个函数中，直到外部有EINT将其cpu唤醒，停下来的代码才继续执行，也就是正常按下了唤醒键的时候。
break;
case PM_SUSPEND_MAX:
MSG(SUSP,"mt6516_pm_enter PM_SUSPEND_MAX/n/r");
MSG(SUSP,"Not support for MT6516/n/r");
break;
default:
MSG(SUSP,"mt6516_pm_enter Error state/n/r");
break;
}
return 0;
}
void mt6516_pm_SuspendEnter(void)
{
UINT32 u32TCM = 0xF0400000;
UINT32 u4SuspendAddr = 0;
UINT32 u4Status, u4BATVol;
UINT32 counter = 0;
/* Check Chip Version*/
if (g_ChipVer == CHIP_VER_ECO_1)
u4SuspendAddr = u32TCM;
else if(g_ChipVer == CHIP_VER_ECO_2)
u4SuspendAddr = __virt_to_phys((unsigned long)MT6516_CPUSuspend);
/*wifi low power optimization : shutdown MCPLL & VSDIO */
wifi_lowpower_opt(TRUE);
/* Check PM related register*/
mt6516_pm_RegDump();
//mt6326_check_power();
DRV_WriteReg32(APMCUSYS_PDN_SET0,0x04200000);
/* STEP7: Set AP_SM_CNF(DxF003C22C) to wanted wake-up source. 设置唤醒源*/
#if defined(PLATFORM_EVB)
mt6516_pm_SetWakeSrc((1<< WS_KP)|(1<<WS_EINT)|(1<<WS_RTC));
#elif defined(PMIC_BL_SETTING)
mt6516_pm_SetWakeSrc((1<<
WS_KP)|(1<<WS_EINT)|(1<<WS_CCIF)|(1<<WS_SM)|(1<<WS_RTC));
#else
mt6516_pm_SetWakeSrc((1<<WS_EINT)|(1<<WS_CCIF)|(1<<WS_SM)|(1<<WS_RTC));
//mt6516_pm_SetWakeSrc((1<<WS_SM));
#endif
/* Save interrupt masks*/
irqMask_L = *MT6516_IRQ_MASKL;
irqMask_H = *MT6516_IRQ_MASKH;
mt6516_pm_Maskinterrupt(); // 20100316 James
while(1)
{
#ifdef AP_MD_EINT_SHARE_DATA
/* Update Sleep flag*/
mt6516_EINT_SetMDShareInfo();
mt6516_pm_SleepWorkAround();
#endif
/* Enter suspend mode, mt6516_slpctrl.s */
if ( g_Sleep_lock <= 0 )
u4Status = MT6516_CPUSuspend (u4SuspendAddr, u32TCM);
else
MSG(SUSP,"Someone lock sleep/n/r");
#ifdef AP_MD_EINT_SHARE_DATA
mt6516_pm_SleepWorkAroundUp();
#endif
/* Check Sleep status*/
u4Status = mt6516_pm_CheckStatus();
if (u4Status == RET_WAKE_TIMEOUT)
{
#ifndef PLATFORM_EVB
DRV_WriteReg32(APMCUSYS_PDN_CLR0,0x04200000);
u4BATVol = (mt6516_pm_GetOneChannelValue(VBAT_CHANNEL,VBAT_COUNT)/VBAT_COUNT);
DRV_WriteReg32(APMCUSYS_PDN_SET0,0x04200000);
MSG(SUSP,"counter = %d, vbat = %d/n/r",counter++, u4BATVol);
if(u4BATVol <= LOW_BAT_ALARM)
{
MSG(SUSP,"Battery Low!!Power off/n/r");
bBAT_UVLO = TRUE;
goto SLP_EXIT;
}
#endif
}
else
{
MSG(SUSP,"leave sleep, wakeup!!/n/r");
goto SLP_EXIT;
//break;
}
}
SLP_EXIT:
wifi_lowpower_opt(FALSE);
/* Restore interrupt mask ; */
*MT6516_IRQ_MASKL = irqMask_L;
*MT6516_IRQ_MASKH = irqMask_H;
}
函数MT6516_CPUSuspend (u4SuspendAddr, u32TCM)是一段汇编代码，在文件：
Kernel/arch/arm/amch-mt6516/mt6516_slpctrl.S中。下面是这段汇编代码片段，看一看也蛮有意思，因为处理进入low power模式之后，是停留在该函数之中的。
ENTRY(MT6516_CPUSuspend)
stmfd sp!, {r4-r12, lr}
// r0 = MT6516_CPUSuspend physical address,
// r1 = TCM address
mov r4, r0
mov r9, r1
// Set SVC mode
mrs r0, cpsr
bic r0, r0, #MODE_MASK1
orr r1, r0, #Mode_SVC
// Set I/F bit, disable IRQ and FIQ
orr r1, r1, #I_Bit|F_Bit
// Update CPSR
msr cpsr_cxsf, r1
// calculate the physical address of instruction after disable MMU
ldr r0, =PhysicalPart
ldr r1, =MT6516_CPUSuspend
sub r0, r0, r1
mov r1, r4
// Now r0 is the physical address of PhysicalPart
add r0, r0, r1
...
...
// Power down Cache and MMU, MCU_MEM_PDN
ldr r0, =0xF0001308
ldr r1, [r0]
// ldr r1, =0xFFFFFFFF
orr r1, r1, #0x0F
str r1, [r0]
// STEP1: Set AP SLEEP (IRQ CODE: 0x36) to level sensitive on CIRQ.
// already done when system start.
// STEP2: Unmask AP SLEEP CTRL interrupt.
// already done at mt6516_pm_Maskinterrupt.
// STEP3: EOI AP SLEEP interrupt.
// already done at mt6516_pm_Maskinterrupt.
// STEP4: Read clear AP_SM_STA (OxF003C21C).
// already done at mt6516_pm_Maskinterrupt.
// STEP5: Set AP_SM_PAUSE_M(0x8003C200) and AP_SM_PAUSE_L(0x8003C204) for sleep duration. 16 seconds as default
...
// STEP6: Set AP_SM_CLK_SETTLE(0xF003C208) to 0x64. Must over 5ms
...
// STEP7: Set AP_SM_CNF(DxF003C22C) to wanted wake-up source. (TP, GPT, MSDC, RTC, EINT, KP or SM)
// already done at mt6516_pm_SuspendEnter
// STEP8: Set AP_SM_CON[1]:PAUSE_START to 1 to enable AP sleep controller.
...
// STEP9: Execute the CP15 command(MCR p15, 0, r0, c7, c0, 4),
// then ARM9 MCU enters low power state
// and STANDBYWFI signal becomes HIGH. CLOCK_OFF signal is issued to Clock Management Unit,
// and then AP MCU Sub-system clock is gated and VCXO OFF signal is issued to AP Sleep Controller.
mov r0, #0
mcr p15, 0, r0,c7,c0,4
// wait till interrupt occurs
// polling AP_SM_STA
mov r2, #0
mov r3, #0x10
15:
//mov r10, r1
// Power up I-Cache
...
//delay
...
// Power up I-Cache upper 16KB
...
//delay
...
// Power up D-Cache
...
//delay
...
// Power up D-Cache upper 16KB
...
//delay
...
// Clean and invalid DCache
// Invalidate instruction cache
// TCM_START_UA saved in r9
mov r2, r9
add r1, r1, r2
// make sure no stall on ¨mov pc,r0〃 below
cmp r1, #0
// restore MMU
mov r4, #0
// access domain 0
// TTB
// flush TLBs
// Turn on MMU
//test
mcr p15, 0, r6, c1, c0, 0
//mov pc, r1
nop
nop
VirtualPart:
nop
nop
mov r0, r10
ldmia sp!, {r4-r12, lr}
mov pc, lr
Nop
六、系统正常suspend和resume时函数调用和配对
enter_state(state)
--> sys_sync()
--> suspend_prepare()
--> pm_prepare_console()
--> pm_notifier_call_chain(PM_SUSPEND_PREPARE)
--> usermodehelper_disable()
--> suspend_freeze_processes()
--> suspend_devices_and_enter(state)
--> suspend_ops->begin(state)
--> _Chip_pm_begin()
--> suspend_console() // 此后串口无信息出来，缓存起来等后面resume打出
--> dpm_suspend_start(PMSG_SUSPEND)
--> dpm_prepare(state)
--> device_prepare(dev, state)
--> dpm_suspend(state)
--> device_suspend(dev, state)
--> suspend_enter(state)
--> suspend_ops->prepare()
--> _Chip_pm_prepare()
--> SetARM9Freq(DIV_4_104)
--> dpm_suspend_noirq(PMSG_SUSPEND)
--> suspend_ops->prepare_late() // 无定义
--> disable_nonboot_cpus()
--> arch_suspend_disable_irqs()
--> sysdev_suspend(PMSG_SUSPEND)
--> suspend_ops->enter(state)
--> _Chip_pm_enter(state)
--> mt6516_pm_SuspendEnter()
--> MT6516_CPUSuspend() // 汇编函数，suspend cpu
<-- MT6516_CPUSuspend() // 汇编函数，resume cpu
<-- mt6516_pm_CheckStatus()
<-- return 0
<-- return 0
<-- sysdev_resume()
<-- arch_suspend_enable_irqs()
<-- enable_nonboot_cpus()
<-- suspend_ops->wake() // 无定义
<-- dpm_resume_noirq(PMSG_RESUME)
<-- suspend_ops->finish()
<-- _Chip_pm_finish()
<-- SetARM9Freq(DIV_1_416)
<-- return 0
<-- return 0
<-- dpm_resume_end(PMSG_RESUME)
<-- dpm_resume(state)
<-- device_resume(dev, state)
<-- dpm_complete(state)
<-- device_complete(dev, state)
<-- resume_console() // 打印出缓存中的信息
<-- suspend_ops->end()
<-- return 0
<-- suspend_finish()
<-- suspend_thaw_processes()
<-- usermodehelper_enable()
<-- pm_notifier_call_chain(PM_POST_SUSPEND)
<-- pm_restore_console()
<-- return 0
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