当手机设备连接PC 电脑时，手机作为peripheral 模式，其开机被枚举的过程大概分为三步：
一次完整的开机 ipc log 如下：

// （1）检测usb cable 插入；
[ 5.862865121] FF extcon idx                   0 ?	
[ 5.868430850] dwc3_msm_vbus_notifier: edev:c440000.qcom,spmi:qcom,pm8150b@2:qcom,usb-pdphy@1700
[ 5.879845642] dwc3_resume_work: resume_work: ext_idx:0
[ 5.879848403] dwc3_resume_work: edev:c440000.qcom,spmi:qcom,pm8150b@2:qcom,usb-pdphy@1700
[ 5.879853142] FF ss_flag                      8 ?	
[ 5.879855798] dwc3_resume_work: max_speed:6 hw_supp_speed:6 override_speed:0
[ 5.879857882] FF speed                        6 ?	
[ 5.879863246] dwc3_ext_event_notify: enter: mdwc->inputs:1 hs_phy_flags:0
[ 5.879865121] dwc3_ext_event_notify: XCVR: ID set
[ 5.879866528] dwc3_ext_event_notify: XCVR: BSV set
[ 5.879867725] dwc3_ext_event_notify: XCVR: SUSP clear
[ 5.879868871] dwc3_ext_event_notify: eud: state:0 active:0 hs_phy_flags:0x0
[ 5.879870642] dwc3_ext_event_notify: exit: mdwc->inputs:3
[ 5.891133663] FF undefined                    0 ?	
[ 5.891135850] FF Exit UNDEF                   0 ?	
[ 5.920572673] FF RT Res                       0 ?	
[ 5.920576684] FF bus_vote_start               1 ?	
[ 5.920902361] FF bus_vote_end                 1 ?	
[ 5.933785955] FF ss_flag                      8 ?	
[ 6.020502518] FF Ctl Res                      0 ?	
[ 6.020506788] FF BIDLE gsync                  1 ?	
[ 6.020508872] FF StrtGdgt gsync               2 ?	
[ 6.021841059] FF VbusSess                     1 ?	
[ 6.021857205] FF StopGdgt psync               1 ?	
[ 6.021862778] FF peripheral                   0 ?	
// （2）开启UDC；
[14.053613792] FF Gadgetstart                  0 ?	
[14.053622230] FF Pullup gsync                 1 ?	
[14.232620824] FF EP0 is not in SETUP phase    0 ?	
[14.246319209] FF run_stop                     1 ?	
[14.276135251] FF __Gadgetstart                0 ?	
[14.280788480] FF UnmaskINT                    0 ?	
[14.287081970] FF Pullup put                   0 ?	
// （3）接收主机的枚举消息，并回应。
[14.313223949] FF BUS RESET                    0 ?	
[14.335765460] FF currentDraw                100 ?	
[14.360327439] FF CONNECT DONE                 4 ?	
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1. 开机枚举

1.1 底层 peripheral

底层识别到 usb cable 插入，产生通知事件到mdwc，mdwc 开启peripheral 模式：

# cat /sys/kernel/debug/ipc_logging/a600000.dwc3/log
[    21.782829232/        0x21faefc3] FF extcon idx                   0 ?	
[    21.782832305/        0x21faeffe] dwc3_msm_vbus_notifier: edev:c440000.qcom,spmi:qcom,pm8150b@2:qcom,usb-pdphy@1700	//pdphy(qcom,usb-pdphy@1700) 挂在pm(qcom,pm8150b@2)下，pm 挂在spmi(c440000.qcom,spmi)下
[    21.782944857/        0x21faf870] dwc3_resume_work: edev:c440000.qcom,spmi:qcom,pm8150b@2:qcom,usb-pdphy@1700
[    21.783028295/        0x21fafeb2] FF speed                        6 ?	
[    21.783039284/        0x21faff84] FF cc_state                     2 ?	
[    21.784039961/        0x21fb4a92] FF undefined                    0 ?	
[    21.784050795/        0x21fb4b61] FF Exit UNDEF                   0 ?	
[    21.784074388/        0x21fb4d27] FF RT Res                       0 ?	
[    21.784093503/        0x21fb4e95] FF bus_vote_start               1 ?	
[    21.784613555/        0x21fb7597] FF bus_vote_end                 1 ?	
[    21.860795639/        0x2211c73f] FF Ctl Res                      0 ?	
[    21.860818451/        0x2211c8f4] FF BIDLE gsync                  1 ?	
[    21.860829493/        0x2211c9c8] FF StrtGdgt gsync               2 ?	
[    21.862160534/        0x22122d9d] FF VbusSess                     1 ?	
[    21.862372826/        0x22123d89] FF StopGdgt psync               1 ?	
[    21.862392409/        0x22123f01] FF peripheral                   0 ?	
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1.1.1 usbpd

\drivers\usb\pd\qpnp-pdphy.c 、policy_engine.c
当 pmic 子系统发生 psy change 事件，会 notify 各个子系统，包括 usbpd:

== pd->psy_nb.notifier_call = psy_changed;		power_supply_reg_notifier(&pd->psy_nb);
	== psy_changed();		//发生了power supply changed notify
		== queue_work(pd->wq, &pd->psy_chg_work);
		== psy_changed_notifier_work();
			== usbpd_process_typec_mode(pd, typec_mode);
			== kick_sm(pd, 0);
				== queue_work(pd->wq, &pd->sm_work);
				== usbpd_sm();
					== state_handlers[pd->current_state].handle_state(pd, rx_msg);
					== enter_state_snk_startup();
						== start_usb_peripheral(pd);
							== extcon_set_state_sync(pd->extcon, EXTCON_USB, 1);
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在 usbpd 中，会创建一个extcon（依赖于一个设备节点），然后其他子系统可以引用该设备节点，并使用该 extcon。

	/*
	 * associate extcon with the parent dev as it could have a DT
	 * node which will be useful for extcon_get_edev_by_phandle()
	 */
	pd->extcon = devm_extcon_dev_allocate(parent, usbpd_extcon_cable);
	if (IS_ERR(pd->extcon)) {
		usbpd_err(&pd->dev, "failed to allocate extcon device\n");
		ret = PTR_ERR(pd->extcon);
		goto put_psy;
	}

	ret = devm_extcon_dev_register(parent, pd->extcon);
	if (ret) {
		usbpd_err(&pd->dev, "failed to register extcon device\n");
		goto put_psy;
	}
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1.1.2 dwc3 & gadget device

== dwc3_msm_vbus_notifier();			dbg_event(0xFF, "extcon idx", enb->idx);
	== queue_work(mdwc->dwc3_wq, &mdwc->resume_work);
	== dwc3_resume_work();
		== dwc3_msm_resume();
		== dwc3_ext_event_notify();
			== queue_delayed_work(mdwc->sm_usb_wq, &mdwc->sm_work, 0);
				== dwc3_otg_sm_work(struct work_struct *w);
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== dwc3_otg_sm_work(struct work_struct *w);
	== dwc3_otg_start_peripheral(mdwc, 1);
		== dwc3_override_vbus_status(mdwc, true);
		== usb_phy_notify_connect(mdwc->hs_phy[0], USB_SPEED_HIGH);
		== usb_gadget_vbus_connect(&dwc->gadget);
			== gadget->ops->vbus_session(gadget, 1);
			== dwc3_gadget_vbus_session(struct usb_gadget *_gadget, int is_active);
				== dwc3_gadget_run_stop_util(dwc);
					== dwc3_gadget_run_stop(struct dwc3 *dwc, int is_on, int suspend);
						== __dwc3_gadget_start(struct dwc3 *dwc);
							== dwc3_writel(dwc->regs, DWC3_GRXTHRCFG, reg);
							== __dwc3_gadget_ep_enable(dep, DWC3_DEPCFG_ACTION_INIT);
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1.2 上层 configfs

上层 init 进程启动，并开启UDC。

echo "a600000.dwc3" > UDC
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[    39.641421266/        0x366af229] FF Gadgetstart                  0 ?	
[    39.641428349/        0x366af2b1] FF Pullup gsync                 1 ?	
[    39.696342724/        0x367b0946] FF EP0 is not in SETUP phase    0 ?	
[    39.696351162/        0x367b09e7] FF run_stop                     1 ?	
[    39.696385433/        0x367b0c79] FF __Gadgetstart                0 ?	
[    39.701054443/        0x367c6aa6] FF UnmaskINT                    0 ?	
[    39.701113610/        0x367c6f16] FF Pullup put                   0 ?	
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（1）绑定gadget 设备与驱动；
（2）start gadget；
（3）pullup gadget。

== gadget_dev_desc_UDC_store();			// \drivers\usb\gadget\configfs.c
	== usb_gadget_probe_driver()	 	// \drivers\usb\gadget\udc\core.c
		== udc_bind_to_driver();		
			== driver->bind(udc->gadget, driver);	
				== configfs_composite_bind();		//绑定usb_gadget 与usb_gadget_driver 
					== usb_add_function(c, f);		//添加function，执行function 的函数
			== usb_gadget_udc_start(udc);
				== udc->gadget->ops->udc_start(udc->gadget, udc->driver);
					== dwc3_gadget_start();
						== request_threaded_irq(irq, dwc3_interrupt, dwc3_thread_interrupt, IRQF_SHARED, "dwc3", dwc->ev_buf);
						//注册dwc3中断，当host发消息过来时，触发中断函数
			== usb_udc_connect_control(struct usb_udc *udc)
				== usb_gadget_connect(struct usb_gadget *gadget)
					== gadget->ops->pullup(gadget, 1);
					== dwc3_gadget_pullup(struct usb_gadget *g, int is_on);
						== dwc3_gadget_run_stop_util();
							== dwc3_gadget_run_stop(dwc, true, false);
								== __dwc3_gadget_start(dwc);		//enable端点传输
									== __dwc3_gadget_ep_enable(struct dwc3_ep *dep, unsigned int action)		// initializes a hw endpoint
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1.3 setup (gadget driver 操作函数）

接收到host 发来的消息，正式开始枚举。

[    39.759129391/        0x368d6e47] FF BUS RESET                    0 ?	
[    39.759165954/        0x368d7104] FF currentDraw                100 ?	
[    39.759205954/        0x368d7403] dwc3_stop_active_transfers: START
[    39.759213141/        0x368d748d] dwc3_stop_active_transfers: DONE
[    39.764147829/        0x368ee6a7] FF CONNECT DONE 
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当端点 enable 之后，即可进行数据传输。
（1）对端点的处理中断；
（2）对设备的处理中断。

	== dwc3_thread_interrupt();					//中断产生（host发消息过来），调用回调函数
		== dwc3_process_event_buf();			//处理中断事件buf(dwc3_event_buffer )
			== dwc3_process_event_entry();		trace_dwc3_event(event->raw, dwc);
				== dwc3_endpoint_interrupt();	//对端点处理的中断
					== dwc3_ep0_interrupt();	//控制传输if (epnum == 0 || epnum == 1) 
						== dwc3_ep0_xfer_complete();		//event->endpoint_event = DWC3_DEPEVT_XFERCOMPLETE
							== dwc3_ep0_inspect_setup();	//dwc->ep0state = EP0_SETUP_PHASE
								//dwc3_ep0_std_request() == dwc3_ep0_set_config()
								== dwc3_ep0_delegate_req();
									== dwc->gadget_driver->setup(&dwc->gadget, ctrl);
									== configfs_composite_setup();	
										== composite_setup();		//setup 包括获取描述符，配置，地址等操作
											== set_config();		//ctrl->bRequest = USB_REQ_SET_CONFIGURATION
					== dwc3_gadget_endpoint_transfer_complete();		//传输完成，返回给function（interface）
						== dwc3_gadget_endpoint_trbs_complete();
							== dwc3_gadget_ep_cleanup_completed_requests()
								== dwc3_gadget_giveback();				//数据返回
									== dwc3_gadget_del_and_unmap_request();		trace_dwc3_gadget_giveback(req);
									== usb_gadget_giveback_request()			trace_usb_gadget_giveback_request(ep, req, 0);// give the request back to the gadget layer
										== req->complete(ep, req);
										== ffs_ep0_complete()	// function的完成函数
				== dwc3_gadget_interrupt(dwc, &event->devt);	//对gadget设备的中断
					== dwc3_gadget_reset_interrupt();				dbg_event(0xFF, "BUS RESET", dwc->gadget.speed);
						== usb_gadget_vbus_draw(&dwc->gadget, 2);	trace_usb_gadget_vbus_draw(gadget, ret);
							== gadget->ops->vbus_draw(gadget, mA);
							== dwc3_gadget_vbus_draw();				dbg_event(0xFF, "currentDraw", mA);
								== dwc3_notify_event(dwc, DWC3_CONTROLLER_SET_CURRENT_DRAW_EVENT, 0);		
					== dwc3_gadget_conndone_interrupt();			dbg_event(0xFF, "CONNECT DONE", speed);

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其中，对端点的处理中断：
\drivers\usb\dwc3\ep0.c

static void dwc3_ep0_xfer_complete(struct dwc3 *dwc,
			const struct dwc3_event_depevt *event)
{
	struct dwc3_ep		*dep = dwc->eps[event->endpoint_number];

	switch (dwc->ep0state) {		//判断ep0 的state
	case EP0_SETUP_PHASE:
		dwc3_ep0_inspect_setup(dwc, event);
		break;

	case EP0_DATA_PHASE:
		dwc3_ep0_complete_data(dwc, event);
		break;

	case EP0_STATUS_PHASE:
		dwc3_ep0_complete_status(dwc, event);
		break;
	default:
		WARN(true, "UNKNOWN ep0state %d\n", dwc->ep0state);
	}
}
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setup 阶段，会响应 host 的各种 req：

== configfs_composite_setup();	
	== composite_setup();		//setup 包括获取描述符，配置，地址等操作
		== set_config();		//ctrl->bRequest = USB_REQ_SET_CONFIGURATION
/*
 * Standard requests, for the bRequest field of a SETUP packet.
 *
 * These are qualified by the bRequestType field, so that for example
 * TYPE_CLASS or TYPE_VENDOR specific feature flags could be retrieved
 * by a GET_STATUS request.
 */
#define USB_REQ_GET_STATUS		0x00
#define USB_REQ_CLEAR_FEATURE		0x01
#define USB_REQ_SET_FEATURE		0x03
#define USB_REQ_SET_ADDRESS		0x05
#define USB_REQ_GET_DESCRIPTOR		0x06
#define USB_REQ_SET_DESCRIPTOR		0x07
#define USB_REQ_GET_CONFIGURATION	0x08
#define USB_REQ_SET_CONFIGURATION	0x09
#define USB_REQ_GET_INTERFACE		0x0A
#define USB_REQ_SET_INTERFACE		0x0B
#define USB_REQ_SYNCH_FRAME		0x0C
#define USB_REQ_SET_SEL			0x30
#define USB_REQ_SET_ISOCH_DELAY		0x31
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