linux suspend/wakeup 如何用于 mach-omap2？

Question

我想弄清楚 suspend/wakeup 是如何为 mach-omap2 实现的，特别是在针对 TI OMAP3530/DM3730.[=17= 的 Linux 2.6.37 中]

下面是一些相关代码：

http://lxr.free-electrons.com/source/arch/arm/mach-omap2/pm34xx.c?v=2.6.37

static int omap3_pm_suspend(void)
{
    struct power_state *pwrst;
    int state, ret = 0;

    if (wakeup_timer_seconds || wakeup_timer_milliseconds)
        omap2_pm_wakeup_on_timer(wakeup_timer_seconds,
                     wakeup_timer_milliseconds);

    /* Read current next_pwrsts */
    list_for_each_entry(pwrst, &pwrst_list, node)
        pwrst->saved_state = pwrdm_read_next_pwrst(pwrst->pwrdm);
    /* Set ones wanted by suspend */
    list_for_each_entry(pwrst, &pwrst_list, node) {
        if (omap_set_pwrdm_state(pwrst->pwrdm, pwrst->next_state))
            goto restore;
        if (pwrdm_clear_all_prev_pwrst(pwrst->pwrdm))
            goto restore;
    }

    omap_uart_prepare_suspend();
    omap3_intc_suspend();

    omap_sram_idle();

restore:
    /* Restore next_pwrsts */
    list_for_each_entry(pwrst, &pwrst_list, node) {
        state = pwrdm_read_prev_pwrst(pwrst->pwrdm);
        if (state > pwrst->next_state) {
            printk(KERN_INFO "Powerdomain (%s) didn't enter "
                   "target state %d\n",
                   pwrst->pwrdm->name, pwrst->next_state);
            ret = -1;
        }
        omap_set_pwrdm_state(pwrst->pwrdm, pwrst->saved_state);
    }
    if (ret)
        printk(KERN_ERR "Could not enter target state in pm_suspend\n");
    else
        printk(KERN_INFO "Successfully put all powerdomains "
               "to target state\n");

    return ret;
}

我真的很难理解它是如何工作的。

看起来，当挂起过程运行到 omap_sram_idle(); 之后，系统已经处于挂起模式，在此函数的上下文中，一切都冻结在那里。当它醒来时，它只是从 restore: 继续并恢复一切。这个对吗？

Answer 1

系统挂起发生在 omap_sram_idle() 的中间。 omap_sram_idle()的第二部分实际上是恢复代码。更准确地说，实际休眠是由 omap34xx_cpu_suspend() 汇编函数中的 wfi ARM 指令完成的。进一步阅读了解详情。

暂停路径

看看omap_sram_idle()函数实现
你可以看到（从注释判断）系统进入休眠前的最后一行是 _omap_sram_idle() call (here)
_omap_sram_idle()指向omap34xx_cpu_suspend() assembler function, which copied previously to SRAM（所以RAM掉电不会丢失）；看看下一行代码：
1. _omap_sram_idle() assignment（注意传递给它的第一个参数是omap34xx_cpu_suspend函数地址）
2. omap_sram_push() implementation; pay attention to memcpy() call：omap_sram_ceil是SRAM内存的起始地址，start是omap34xx_cpu_suspend() function
3. omap34xx_cpu_suspend() implementation; it's the actual function being executed at this line（而不是 _omap_sram_idle()）。看看这个函数上面的评论：
```
/*
 * Forces OMAP into idle state
 *
 * omap34xx_suspend() - This bit of code just executes the WFI
 * for normal idles.
 *
 * Note: This code get's copied to internal SRAM at boot. When the OMAP
 *       wakes up it continues execution at the point it went to sleep.
 */
```
实际休眠发生在wfi（等待中断）ARM指令中（在omap34xx_cpu_suspend()函数中）；处理器会休眠，只有在某些 IRQ 发生时才会唤醒
omap34xx_cpu_suspend()有2个地方可以执行wfi：
- 如果不需要上下文保存：here
- 如果需要上下文保存：here

还原路径

一旦发生唤醒信号，CPU 将继续执行 wfi 指令之后的指令（首先将其置于睡眠状态）。所以你的系统在 omap34xx_cpu_suspend() 汇编函数中唤醒（从 wait_sdrk_ok: 标签开始），然后 returns 回到 omap_sram_idle() （到 this 行），然后 returns 回到 omap3_pm_suspend()，回到 restore: 标签。

linux suspend/wakeup 如何用于 mach-omap2？

How linux suspend/wakeup works for mach-omap2?

linux

arm

omap

linux-kernel

暂停路径

还原路径