高通平台android 8.1基线某款usb camera打开dev/video1出错

故障现象：
某客户需要调试一款usb camera，包括黑白和彩色两个sensor：

在调试中发现调用open函数去打开注册的 dev/video1节点时报错：
USBCamera: Cannot open ‘/dev/video1’: 16, Device or resource busy

分析：
1.首先排查硬件的问题。
把该camera连接到PC，下载通用的camera驱动后，设备管理器中显示：

使用网上下载的USB摄像头采集调试工具2020可以正常使用的，说明硬件是好的。

2.检查下camera的uvc驱动注册是正常的:
[ 6.406765] usb 1-1: New USB device found, idVendor=15aa, idProduct=1555
[ 6.412464] usb 1-1: New USB device strings: Mfr=3, Product=1, SerialNumber=2
[ 6.419546] usb 1-1: Product: SIT USB2.0 Camera RGB
[ 6.424433] usb 1-1: Manufacturer: Generic
[ 6.428487] usb 1-1: SerialNumber: 200901010001
[ 6.439198] uvcvideo: Found UVC 1.00 device SIT USB2.0 Camera RGB (15aa:1555)
检查dev下成功注册了video1节点。

3.apk会通过ioctl调到uvc camera的open操作。（uvc_v4l2.c）

const struct v4l2_file_operations uvc_fops = {.owner        = THIS_MODULE,.open        = uvc_v4l2_open,.release   = uvc_v4l2_release,.unlocked_ioctl = uvc_v4l2_ioctl,
#ifdef CONFIG_COMPAT.compat_ioctl32 = uvc_v4l2_compat_ioctl32,
#endif.read     = uvc_v4l2_read,.mmap      = uvc_v4l2_mmap,.poll      = uvc_v4l2_poll,
#ifndef CONFIG_MMU.get_unmapped_area = uvc_v4l2_get_unmapped_area,
#endif
};

既然是上层open错误，那肯定是调用到驱动这里的open有错误。
继续添加打印发现是uvc_fops的.open函数uvc_v4l2_open -->ret = usb_autopm_get_interface(stream->dev->intf);
这里返回错误 -16。

4.usb_autopm_get_interface分析。
uvc_v4l2_open函数里会调用usb_autopm_get_interface：

static int uvc_v4l2_open(struct file *file)
{struct uvc_streaming *stream;struct uvc_fh *handle;int ret = 0;uvc_trace(UVC_TRACE_CALLS, "uvc_v4l2_open\n");stream = video_drvdata(file);if (stream->dev->state & UVC_DEV_DISCONNECTED)return -ENODEV;ret = usb_autopm_get_interface(stream->dev->intf);if (ret < 0)return ret;/* Create the device handle. */handle = kzalloc(sizeof *handle, GFP_KERNEL);if (handle == NULL) {usb_autopm_put_interface(stream->dev->intf);return -ENOMEM;}mutex_lock(&stream->dev->lock);if (stream->dev->users == 0) {ret = uvc_status_start(stream->dev, GFP_KERNEL);if (ret < 0) {mutex_unlock(&stream->dev->lock);usb_autopm_put_interface(stream->dev->intf);kfree(handle);return ret;}}stream->dev->users++;mutex_unlock(&stream->dev->lock);v4l2_fh_init(&handle->vfh, stream->vdev);v4l2_fh_add(&handle->vfh);handle->chain = stream->chain;handle->stream = stream;handle->state = UVC_HANDLE_PASSIVE;file->private_data = handle;return 0;
}

这里就得说一下设备驱动的休眠和唤醒。
usb的驱动结构体中有一个flag：.supports_autosuspend ，用来标识是否支持自动休眠。当USB某个接口繁忙或空闲时通知USB core。主要有如下6个函数来实现休眠、唤醒功能：
int usb_autopm_get_interface(struct usb_interface *intf);
void usb_autopm_put_interface(struct usb_interface *intf);
int usb_autopm_get_interface_async(struct usb_interface *intf);
void usb_autopm_put_interface_async(struct usb_interface *intf);
void usb_autopm_get_interface_no_resume(struct usb_interface *intf);
void usb_autopm_put_interface_no_suspend(struct usb_interface *intf);
这些函数通过维护使用计数器来工作。当计数器大于0时，接口将被视为繁忙，内核不会进入autosuspend；当usage counter=0时，接口被认为是空闲的，内核将会进入autosuspend。

重点关注 usb_autopm_get_interface和usb_autopm_put_interface函数。

/*** usb_autopm_get_interface - increment a USB interface's PM-usage counter* @intf: the usb_interface whose counter should be incremented** This routine should be called by an interface driver when it wants to* use @intf and needs to guarantee that it is not suspended.  In addition,* the routine prevents @intf from being autosuspended subsequently.  (Note* that this will not prevent suspend events originating in the PM core.)* This prevention will persist until usb_autopm_put_interface() is called* or @intf is unbound.  A typical example would be a character-device* driver when its device file is opened.** @intf's usage counter is incremented to prevent subsequent autosuspends.* However if the autoresume fails then the counter is re-decremented.** This routine can run only in process context.** Return: 0 on success.*/
int usb_autopm_get_interface(struct usb_interface *intf)
{int    status;status = pm_runtime_get_sync(&intf->dev);if (status < 0)pm_runtime_put_sync(&intf->dev);elseatomic_inc(&intf->pm_usage_cnt);dev_vdbg(&intf->dev, "%s: cnt %d -> %d\n",__func__, atomic_read(&intf->dev.power.usage_count),status);if (status > 0)status = 0;return status;
}

●usb_autopm_get_interface将会让usage counter +1，并在设备已经进入suspend时执行autoresume；如果autoresume失败，计数器又会-1到初始值的。

/*** usb_autopm_put_interface - decrement a USB interface's PM-usage counter* @intf: the usb_interface whose counter should be decremented** This routine should be called by an interface driver when it is* finished using @intf and wants to allow it to autosuspend.  A typical* example would be a character-device driver when its device file is* closed.** The routine decrements @intf's usage counter.  When the counter reaches* 0, a delayed autosuspend request for @intf's device is attempted.  The* attempt may fail (see autosuspend_check()).** This routine can run only in process context.*/
void usb_autopm_put_interface(struct usb_interface *intf)
{struct usb_device  *udev = interface_to_usbdev(intf);int          status;usb_mark_last_busy(udev);atomic_dec(&intf->pm_usage_cnt);status = pm_runtime_put_sync(&intf->dev);dev_vdbg(&intf->dev, "%s: cnt %d -> %d\n",__func__, atomic_read(&intf->dev.power.usage_count),status);
}

●usb_autopm_put_interface执行和usb_autopm_get_interface相反的功能，让usage counter -1，如果usage counter =0，则进入autosuspend。
简单说，就是在驱动的open里调用usb_autopm_get_interface，在close里调用usb_autopm_put_interface，以此来实现usb的休眠唤醒功能。

回到前面的问题，usb_autopm_get_interface返回错误：-16，说明该usb camera的休眠唤醒有问题，camera无法被唤醒。根据网上的参考怀疑echi处于suspend状态导致camera无法正常open, 由于项目不需要考虑耗电,所以打算暂时去掉pm runtime的功能： #CONFIG_PM_RUNTIME is not set
尴尬的是，android 8.1上注掉CONFIG_PM_RUNTIME会导致kernel编译不过的，使用CONFIG_PM_RUNTIME宏控制的代码很多，这样修改的工作量很大。

继续检查代码，在usb_enumerate_device函数中注释掉port进入休眠就可以正常了：

static int usb_enumerate_device(struct usb_device *udev)
{int err;struct usb_hcd *hcd = bus_to_hcd(udev->bus);if (udev->config == NULL) {err = usb_get_configuration(udev);if (err < 0) {if (err != -ENODEV)dev_err(&udev->dev, "can't read configurations, error %d\n",err);return err;}}/* read the standard strings and cache them if present */udev->product = usb_cache_string(udev, udev->descriptor.iProduct);udev->manufacturer = usb_cache_string(udev,udev->descriptor.iManufacturer);udev->serial = usb_cache_string(udev, udev->descriptor.iSerialNumber);err = usb_enumerate_device_otg(udev);if (err < 0)return err;if (IS_ENABLED(CONFIG_USB_OTG_WHITELIST) && hcd->tpl_support &&!is_targeted(udev)) {/* Maybe it can talk to us, though we can't talk to it.* (Includes HNP test device.)*/if (IS_ENABLED(CONFIG_USB_OTG) && (udev->bus->b_hnp_enable|| udev->bus->is_b_host)) {//stone：注释掉usb的休眠//err = usb_port_suspend(udev, PMSG_AUTO_SUSPEND);if (err < 0)dev_dbg(&udev->dev, "HNP fail, %d\n", err);}return -ENOTSUPP;}usb_detect_interface_quirks(udev);return 0;
}

如果还是打不开，还需要考虑下应用的尺寸设置是否合适。

可以参考：https://www.kernel.org/doc/html/v4.16/driver-api/usb/power-management.html

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