USB設備狀態設置-- usb_gadget_set_state()

1、USB設備狀態

在USB 2.0協議中第 9.1 USB Device States 章節規定了USB設備的6種狀態，包括：

Attached/Powered/Default/Address/Configured/Suspended

其狀態遷移圖以下：

在 Linux Kernel ch9.h 文件中用 enum usb_device_state 來標記這幾種狀態。

// <kernel_dir>/include/uapi/linux/usb/ch9.h

enum usb_device_state {
    /* NOTATTACHED isn't in the USB spec, and this state acts
     * the same as ATTACHED ... but it's clearer this way.
     */
    USB_STATE_NOTATTACHED = 0,

    /* chapter 9 and authentication (wireless) device states */
    USB_STATE_ATTACHED,
    USB_STATE_POWERED,          /* wired */
    USB_STATE_RECONNECTING,         /* auth */
    USB_STATE_UNAUTHENTICATED,      /* auth */
    USB_STATE_DEFAULT,          /* limited function */
    USB_STATE_ADDRESS,
    USB_STATE_CONFIGURED,           /* most functions */

    USB_STATE_SUSPENDED

    /* NOTE:  there are actually four different SUSPENDED
     * states, returning to POWERED, DEFAULT, ADDRESS, or
     * CONFIGURED respectively when SOF tokens flow again.
     * At this level there's no difference between L1 and L2
     * suspend states.  (L2 being original USB 1.1 suspend.)
     */
};

2、狀態設置函數usb_gadget_set_state()

// <kernel_dir>/drivers/usb/gadget/udc/udc-core.c

void usb_gadget_set_state(struct usb_gadget *gadget,
        enum usb_device_state state)
{
    gadget->state = state;
    schedule_work(&gadget->work);
}
EXPORT_SYMBOL_GPL(usb_gadget_set_state);

// <kernel_dir>/include/linux/usb/gadget.h
extern void usb_gadget_set_state(struct usb_gadget *gadget,  enum usb_device_state state);

在 udc-core.c 文件中，會去定義usb_gadget_set_state()函數，將狀態state的值賦值給gadget->state。其中struct usb_gadget是用來標記一個USB設備的信息。此時USB設備的狀態就能夠肯定了。以後啓動工做隊列schedule_work(&gadget->work);將狀態信息給到sysfs。

在USB的枚舉階段，會根據USB所處的狀態調用usb_gadget_set_state()去設置USB設備的狀態。
好比說在USB設備的枚舉階段，在composite_setup()函數中USB設備接收到了USB Host發過來的USB_REQ_SET_CONFIGURATION命令後調用set_config()設置相應的配置，這以後就會調用usb_gadget_set_state()去設置爲USB_STATE_CONFIGURED狀態。

3、usb_gadget_state_work()

// <kernel_dir>/drivers/usb/gadget/udc/udc-core.c

* usb_add_gadget_udc_release - adds a new gadget to the udc class driver list
 * @parent: the parent device to this udc. Usually the controller driver's
 * device.
 * @gadget: the gadget to be added to the list.
 * @release: a gadget release function.
 *
 * Returns zero on success, negative errno otherwise.
 */
int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
        void (*release)(struct device *dev))

在usb_add_gadget_udc_release()中會去綁定 gadget->work 到 usb_gadget_state_work() 函數。

static void usb_gadget_state_work(struct work_struct *work)
{
    struct usb_gadget *gadget = work_to_gadget(work);
    struct usb_udc *udc = gadget->udc;

    if (udc)
        sysfs_notify(&udc->dev.kobj, NULL, "state");
}

這個函數主要目的就是將當前的 state 信息寫入到 sysfs 中去。這個信息能夠cat出來。

#cat /sys/devices/platform/xxx_udc/state

路徑不徹底是這個，可是在 /sys/devices 目錄下會有對應udc控制器 xxx_udc 的狀態節點。不只包含狀態的節點，還包含其餘的信息。

-r--r--r-- 0        0              4096 2017-05-01 16:17 a_alt_hnp_support
-r--r--r-- 0        0              4096 2017-05-01 16:17 a_hnp_support
-r--r--r-- 0        0              4096 2017-05-01 16:17 b_hnp_enable
-r--r--r-- 0        0              4096 2017-05-01 16:17 current_speed
lrwxrwxrwx 0        0               2017-05-01 16:17 device -> ../../../panasonic_udc.1
-r--r--r-- 0        0              4096 2017-05-01 16:17 is_a_peripheral
-r--r--r-- 0        0              4096 2017-05-01 16:17 is_otg
-r--r--r-- 0        0              4096 2017-05-01 16:17 maximum_speed
drwxr-xr-x 0        0                   2017-05-01 16:17 power
--w------- 0        0              4096 2017-05-01 16:17 soft_connect
--w------- 0        0              4096 2017-05-01 16:17 srp
-r--r--r-- 0        0              4096 2017-05-01 16:17 state
lrwxrwxrwx 0        0                   2017-05-01 16:17 subsystem -> ../../../../../class/udc
-rw-r--r-- 0        0              4096 2017-05-01 16:17 uevent

這裏面的信息其實就是一個USB設備的信息，用 struct usb_gadget 來描述。關於USB Gadget的內容將在後續的文章中整理出來。