参考文件：
kernel/drivers/usb/phy/phy-msm-usb.c
kernel/msm-3.18/drivers/usb/phy/phy-msm-usb.c

+//begin:stone modify for usb id
+static bool usb_id_flag = 1;
+bool get_usb_id(void)
+{
+	return usb_id_flag;
+}
+EXPORT_SYMBOL(get_usb_id);
+//end:stone modify for usb id

在msm_id_status_w函数中添加即可：

static void msm_id_status_w(struct work_struct *w)
{
	struct msm_otg *motg = container_of(w, struct msm_otg,
						id_status_work.work);
	int work = 0;
	int id_state = 0;

	dev_dbg(motg->phy.dev, "ID status_w\n");

	if (motg->pdata->pmic_id_irq)
		id_state = msm_otg_read_pmic_id_state(motg);
	else if (motg->ext_id_irq)
		id_state = gpio_get_value(motg->pdata->usb_id_gpio);
	else if (motg->phy_irq)
		id_state = msm_otg_read_phy_id_state(motg);
		//usb_otg: usb@78d9000 {中定义了：
		//interrupt-names = "core_irq", "async_irq","phy_irq";
		//motg->phy_irq = platform_get_irq_byname(pdev, "phy_irq");
		//所以phy_irq不为空，走到这里
		
	if (id_state) {
		if (!test_and_set_bit(ID, &motg->inputs)) {
			pr_debug("ID set\n");
			msm_otg_dbg_log_event(&motg->phy, "ID SET",
					motg->inputs, motg->phy.state);
			work = 1;
		}
	} else {
		if (test_and_clear_bit(ID, &motg->inputs)) {
			pr_debug("ID clear\n");
			msm_otg_dbg_log_event(&motg->phy, "ID CLEAR",
					motg->inputs, motg->phy.state);
			set_bit(A_BUS_REQ, &motg->inputs);
			work = 1;
		}
	}

	+//begin:stone modify for usb id
	+usb_id_flag = !!id_state;
	+printk(KERN_ERR "usb_id_flag=%d\n",usb_id_flag);
	+//end:stone modify for usb id

	if (work && (motg->phy.state != OTG_STATE_UNDEFINED)) {
		msm_otg_dbg_log_event(&motg->phy,
				"CHECK ID EVENT DURING SUSPEND",
				atomic_read(&motg->pm_suspended),
				motg->sm_work_pending);
		if (atomic_read(&motg->pm_suspended)) {
			motg->sm_work_pending = true;
		} else if (!motg->sm_work_pending) {
			/* process event only if previous one is not pending */
			queue_work(motg->otg_wq, &motg->sm_work);
		}
	}

}

真正读取ID的函数是msm_otg_read_phy_id_state：

static bool msm_otg_read_phy_id_state(struct msm_otg *motg)
{
	u8 val;

	/*
	 * clear the pending/outstanding interrupts and
	 * read the ID status from the SRC_STATUS register.
	 */
	writeb_relaxed(USB_PHY_ID_MASK, USB2_PHY_USB_PHY_INTERRUPT_CLEAR1);

	writeb_relaxed(0x1, USB2_PHY_USB_PHY_IRQ_CMD);
	/*
	 * Databook says 200 usec delay is required for
	 * clearing the interrupts.
	 */
	udelay(200);
	writeb_relaxed(0x0, USB2_PHY_USB_PHY_IRQ_CMD);

	val = readb_relaxed(USB2_PHY_USB_PHY_INTERRUPT_SRC_STATUS);
	if (val & USB_PHY_IDDIG_1_0)
		return false; /* ID is grounded */
	else
		return true;
}