android 9.0上usb otg休眠问题

问题：手机作为otg host时，怎样才能进入待机休眠？

参考高通文档：《80-NF283-1_C_Linux_USB_Implementation_Guide》
section: 7.1.2 Host mode state transition
As shown in Figure 7-1, the USB enters LPM when:
●The USB A-Cable is removed, with or without a B-Device connected.
●USB bus suspend – USB Host mode provides the Autosuspend feature via CONFIG_USB_SUSPEND, defined by default. The host controller driver monitors each device connected on the bus and, if any device is idle for a period more than a predefined timeout, it selectively suspends the device. However, if any one of the drivers corresponding to an interface in the USB device does not support Autosuspend, the device cannot be suspended. The mass storage driver does not support Autosuspend.Hence, if a mass storage device is connected, it is not suspended. The HUB driver supports Autosuspend. More information is available at Documentation/usb/power-management.txt.

高通case回复Answer:
Linux Android USB host driver stack(UHCI&EHCI&XHCI) have support for suspend/power collapse, but most device class drivers do not enabled auto suspend. We need to enable autosuspend for those devices,can call usb_enable_autosuspend() function in the driver device probe routine.

An example for HID device is as below:（如下的例子是一个HID设备休眠的修改）

drivers/hid/usbhid/hid-core.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
index ff052c8…399d964 100644
— a/drivers/hid/usbhid/hid-core.c
+++ b/drivers/hid/usbhid/hid-core.c
@@ -1338,6 +1338,9 @@ static int usbhid_probe(struct usb_interface *intf, const struct usb_device_id *
goto err_free;
}

+/* enable suspend/resume support for HID devices. */
+usb_enable_autosuspend(dev);

return 0;
err_free:
kfree(usbhid);
@@ -1349,11 +1352,13 @@ err:
static void usbhid_disconnect(struct usb_interface *intf)
{
struct hid_device *hid = usb_get_intfdata(intf);
+struct usb_device *dev = interface_to_usbdev(intf);
struct usbhid_device *usbhid;

if (WARN_ON(!hid))
return;

+usb_disable_autosuspend(dev);
usbhid = hid->driver_data;
hid_destroy_device(hid);
kfree(usbhid);
按照上面的修改后，otg侧连上鼠标是可以进入休眠了，主机功耗满足要求；点击鼠标是可以正常唤醒手机的。

注意点1：
on 8994/8992, host bus suspend is not supported due to some HW issue.

static int dwc3_otg_start_host(struct usb_otg *otg, int on)
{…
/**
*WORKAROUND: currently host mode suspend isn't working well.
*Disable xHCI's runtime PM for now.
*/
pm_runtime_disable(&dwc->xhci->dev);

注意点2：
需要检查设备是否支持remotewakeup，如果不支持的话，autosuspend就不会执行下去的。autosuspend_check函数会去检查设备是否支持remotewakeup：

if (w && !device_can_wakeup(&udev->dev)) {dev_dbg(&udev->dev, "remote wakeup needed for autosuspend\n");
return -EOPNOTSUPP;
}

看这个结构体:

static const struct dev_pm_ops usb_device_pm_ops = {.prepare = usb_dev_prepare,.complete = usb_dev_complete,.suspend = usb_dev_suspend,.resume = usb_dev_resume,.freeze = usb_dev_freeze,.thaw =  usb_dev_thaw,.poweroff = usb_dev_poweroff,.restore = usb_dev_restore,.runtime_suspend = usb_runtime_suspend,.runtime_resume = usb_runtime_resume,.runtime_idle =  usb_runtime_idle,
};

在执行suspend的函数usb_runtime_suspend中会去检查设备是否支持remotewakeup ：
usb_runtime_suspend -->

 if (autosuspend_check(udev) != 0)return -EAGAIN;

如果不支持remotewakeup ，autosuspend就不会执行。

autosuspend_check -->

if (w && !device_can_wakeup(&udev->dev)) {dev_dbg(&udev->dev, "remote wakeup needed for autosuspend\n");return -EOPNOTSUPP;}

device_can_wakeup读取的是设备模型中的成员：can_wakeup
（include/Linux/pm.h文件）

struct dev_pm_info {pm_message_t power_state;
unsigned can_wakeup:1;
#ifdef CONFIG_PM
unsigned should_wakeup:1;
pm_message_t prev_state;
void * saved_state;
struct device * pm_parent;
struct list_head entry;
#endif
};

在配置描述符中，USB设备将是否支持remote wakeup的能力报告给主机。在设备注册时赋值给can_wakeup的。

移远EC20模块的功能说明：

这里说的是如果主机不支持usb remote wakeup就需要RI信号来唤醒主机，因为这样情况下主机的usb控制器, phy都可以进入休眠状态。关闭相关clock时钟, 甚至断电，必须通过外部中断来唤醒；

如果需要支持usb remote wakeup, 则主机侧不能完全断电, 需要留下部分底电流, 当usb外设发出request wakeup请求后, 能通过usbphy->usb controller->cpu 将整体系统唤醒。 (常见如个人电脑产品, 基本都支持usb鼠标键盘唤醒)

由于设备都是被动响应主机的命令，想要进入suspend状态，就要控制主机不要发数据包以及令牌包。USB在上行总线上监测到一个连续的空闲状态至少持续了3.0ms时，开始转入挂起状态，在总线无活动后的10ms内被真正挂起。主机可以通过停止所有的传输(包括SOF令牌包)来启动全局挂起，或者是通过主机向集线器端口发出SetPortFeature请求来实现选择性挂起。

8953作为otg连接usb modem的休眠
usb modem连接8953注册的是tty设备，对应驱动在：
kernel/msm-4.9/drivers/usb/serial/usb-serial.c
按照高通的修改，需要在probe函数中使能autosuspend。

diff --git a/kernel/msm-4.9/drivers/usb/serial/usb-serial.c b/kernel/msm-4.9/drivers/usb/serial/usb-serial.c
old mode 100644
new mode 100755
index 4a037b4a79..761968f839
--- a/kernel/msm-4.9/drivers/usb/serial/usb-serial.c
+++ b/kernel/msm-4.9/drivers/usb/serial/usb-serial.c
@@ -1080,6 +1080,14 @@ static int usb_serial_probe(struct usb_interface *interface,if (num_ports > 0)usb_serial_console_init(serial->port[0]->minor);
+
+       //stone added
+       /* enable suspend/resume support */
+       if (device_can_wakeup(&dev->dev)) {+               printk(KERN_ERR "-----sy:usb device can remote wakeup------\n");
+       }
+       usb_enable_autosuspend(dev);
+exit:module_put(type->driver.owner);return 0;
@@ -1098,6 +1106,9 @@ static void usb_serial_disconnect(struct usb_interface *interface)struct usb_serial_port *port;struct tty_struct *tty;+       //stone added
+       struct usb_device *usb_dev = interface_to_usbdev(interface);
+usb_serial_console_disconnect(serial);mutex_lock(&serial->disc_mutex);
@@ -1121,6 +1132,9 @@ static void usb_serial_disconnect(struct usb_interface *interface)if (serial->type->disconnect)serial->type->disconnect(serial);+       //stone added
+       usb_disable_autosuspend(usb_dev);
+/* let the last holder of this object cause it to be cleaned up */usb_serial_put(serial);dev_info(dev, "device disconnected\n");

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