UDC-Gadget

UDC：(USB Device Controller)用于管理和控制USB设备与主机之间的通信。
Gadget：Android在此层实现了adb，mtp(Media Transfer Protocol 媒体传输协议)，mass_storage等。

早期的USB只支持单一的gadget设备，使用场景较为简单，随后加入了composite framework，用来支持多个function的gadget设备，多个function的绑定在内核中完成，若需要修改，则需要修改内核，不灵活也不方便。Linux3.11版本引入了基于configfs的usb gadget configfs。
usb gadget configfs重新实现了复合设备层，可以在用户空间配置和组合内核的function，灵活的构成USB复合设备，极大了提高了工作效率。
system/core/rootdir/init.usb.configfs.rc

[persist.sys.usb.config]: [diag,adb]
[sys.usb.config]: [mtp,adb] on property:sys.usb.ffs.ready=1 && property:sys.usb.config=mtp,adb && property:sys.usb.configfs=1write /config/usb_gadget/g1/configs/b.1/strings/0x409/configuration "mtp_adb"write /config/usb_gadget/g1/idVendor 0x0c2ewrite /config/usb_gadget/g1/idProduct 0x0ba3symlink /config/usb_gadget/g1/functions/mtp.gs0 /config/usb_gadget/g1/configs/b.1/f1symlink /config/usb_gadget/g1/functions/ffs.adb /config/usb_gadget/g1/configs/b.1/f2write /config/usb_gadget/g1/UDC ${sys.usb.controller}setprop sys.usb.state ${sys.usb.config}

drivers/usb/gadget/configfs.c
drivers\usb\gadget\composite.c
drivers/usb/gadget/udc/core.c
drivers/usb/gadget/function/f_mtp.c
USB总线-Linux内核USB3.0设备控制器复合设备之USB gadget configfs分析

gadget -> composite -> functionmake_group -> function_make -> usb_get_function_instance -> alloc_inst -> mtp_alloc_inst
每个function driver创建的时候会分配一个usb_function_instanceecho  4e00000.dwc3 >  configs/usb_gadget/g1/UDC 
usb_udc_attch_driver-> udc_bind_to_driver-> configfs_composite_bind -> usb_add_function -> function->bind -> mtp_function_bind

HCD-XHCI

HCD：(Host Controller Driver)是主机控制器驱动，它是对主机控制器硬件的抽象。
XHCI：(eXtensible Host Controller Interface)也是主机控制器驱动，XHIC是基于USB3.0并且向下兼容，其中集成了两个roothub，一个对应usb2.0的(main_hcd)，一个对应usb3.0的(shared_hcd)

struct xhci_hcd {/* usb_hcd结构体：用于描述USB主机控制器驱动*/struct usb_hcd *main_hcd;struct usb_hcd *shared_hcd;/* glue to PCI and HCD framework */struct xhci_cap_regs __iomem *cap_regs;struct xhci_op_regs __iomem *op_regs;struct xhci_run_regs __iomem *run_regs;struct xhci_doorbell_array __iomem *dba;/* Our HCD's current interrupter register set */struct	xhci_intr_reg __iomem *ir_set;/* Cached register copies of read-only HC data */__u32		hcs_params1;...spinlock_t	lock;/* packed release number */u8		sbrn;u16		hci_version;.........};

root hub设备注册(三)
drivers/usb/host/xhci-plat.c
drivers/usb/core/hcd.c
drivers/usb/host/xhci.c
drivers/usb/core/hub.c


dwc3_otg_start_host ->   dwc3_host_init -> platform_device_add(xhci) -> xhci_plat_probexhci->main_hcd = hcd;  
usb_add_hcd(hcd, irq, IRQF_SHARED); //roothub对应usb0
usb_add_hcd(xhci->shared_hcd, irq, IRQF_SHARED);hcd->driver->start(hcd)  //hc_driverxhci_run(hcd)xhci_try_enable_msi(hcd)hci_setup_msix(xhci)xhci_irq(hcd)---------------------------------------------------------------------------------|	xhci_handle_event(xhci)														||	case: TRB_PORT_STATUS                                                       ||		handle_port_status(xhci, event);                                        ||	case: TRB_TRANSFER                                                          ||		handle_tx_event(xhci, &event->trans_event);                             ||			usb_hcd_giveback_urb                                                ||				tasklet_schedule(&bh->bh);                                      ||					kick_hub_wq(hub);                                           ||						queue_work(hub_wq, &hub->events)                        ||							hub_event->port_event->hub_port_connect_change      ||								->hub_port_connect -> usb_new_device(udev);     |----------------------------------------------------------------------------------		register_root_hub(hcd)usb_get_device_descriptor(usb_dev, USB_DT_DEVICE_SIZE)usb_new_device (usb_dev)usb_enumerate_device(udev)announce_device(udev)/* 打印New USB device found*/device_add(&udev->dev)

DWC3

DWC3：(DesignWare USB 3.0 Controller) 在Android系统中，dwc3通常被用作USB3.0主机控制器，用于与XHCI驱动程序配合使用，控制USB3.0设备与主机之间的通信。同时，dwc3还可以与Gadget驱动程序配合使用，将linux设备转为USB设备，实现设备与主机间的通信。
dwc3控制器初始化的时候会将控制器设置为USB_DR_MODE_OTG模式，同时调用dwc3_host_init和dwc3_gadget_init函数初始化主机模式和设备模式所需的资源，控制器后续可以动态切换为主机模式和设备模式。

                  ->   host mode    xhci   dwc3_host_init()
dwc3 controller -->   device mode  udc    dwc3_gadget_init()dual-role device (DRD) OTG State
enum dwc3_drd_state {DRD_STATE_UNDEFINED = 0, //put controller and phy in suspend if no cable connected//pm_runtime_putsync decrease usage_countDRD_STATE_IDLE,	         DRD_STATE_PERIPHERAL,DRD_STATE_PERIPHERAL_SUSPEND,DRD_STATE_HOST_IDLE,DRD_STATE_HOST,};
dual-role usb control(DR) works on a particular mode
enum usb_dr_mode {USB_DR_MODE_UNKNOWN,USB_DR_MODE_HOST,USB_DR_MODE_PERIPHERAL,USB_DR_MODE_OTG,};状态的切换通过dwc3_otg_sm_work -> dwc3_otg_start_host/dwc3_otg_start_peripheral

power/supply/qcom/qpnp-smb5.c devm_extcon_dev_register 发送广播

static const unsigned int smblib_extcon_cable[] = {EXTCON_USB,EXTCON_USB_HOST,EXTCON_NONE,
};smblib_notify_device_modeextcon_set_state_sync(chg->extcon, EXTCON_USB, enable);
smblib_notify_usb_hostextcon_set_state_sync(chg->extcon, EXTCON_USB_HOST, enable);

usb/dwc3/dwc3-msm.c devm_extcon_register_notifier注册监听usb状态变化，接受广播

mdwc->extcon[idx].vbus_nb.notifier_call = dwc3_msm_vbus_notifier;
extcon_register_notifier(edev, EXTCON_USB, &mdwc->extcon[idx].vbus_nb);
extcon_register_notifier(edev, EXTCON_USB_HOST,&mdwc->extcon[idx].id_nb);
dwc3_msm_vbus_notifier(&mdwc->extcon[idx].vbus_nb,true, edev);
dwc3_msm_id_notifier(&mdwc->extcon[idx].id_nb,true, edev);