linux usb host 读阻塞

问题：usb host 读数据的时候阻塞在 wait_for_completion(&dev->bulk_in_completion);

解决办法：将 wait_for_completion 替换成用等待队列（waitqueue），步骤如下

@@ -61,11 +61,10 @@ struct usb_skel { __u8bulk_out_endpointAddr;/* the address of the bulk out endpoint */ interrors;/* the last request tanked */ boolongoing_read;/* a read is going on */-boolprocessed_urb;/* indicates we haven't processed the urb */ spinlock_terr_lock;/* lock for errors */ struct krefkref; struct mutexio_mutex;/* synchronize I/O with disconnect */-struct completionbulk_in_completion;/* to wait for an ongoing read */+wait_queue_head_tbulk_in_wait;/* to wait for an ongoing read */ }; #define to_skel_dev(d) container_of(d, struct usb_skel, kref) @@ -185,7 +184,7 @@ static void skel_read_bulk_callback(struct urb *urb) dev->ongoing_read = 0; spin_unlock(&dev->err_lock); -complete(&dev->bulk_in_completion);+wake_up_interruptible(&dev->bulk_in_wait); }  static int skel_do_read_io(struct usb_skel *dev, size_t count)@@ -206,13 +205,16 @@ static int skel_do_read_io(struct usb_skel *dev, size_t count) dev->ongoing_read = 1; spin_unlock_irq(&dev->err_lock); +/* submit bulk in urb, which means no data to deliver */+dev->bulk_in_filled = 0;+dev->bulk_in_copied = 0;+ /* do it */ rv = usb_submit_urb(dev->bulk_in_urb, GFP_KERNEL); if (rv < 0) { dev_err(&dev->interface->dev, "%s - failed submitting read urb, error %d\n", __func__, rv);-dev->bulk_in_filled = 0; rv = (rv == -ENOMEM) ? rv : -EIO; spin_lock_irq(&dev->err_lock); dev->ongoing_read = 0;@@ -261,25 +263,9 @@ retry:  * IO may take forever  * hence wait in an interruptible state  */-rv = wait_for_completion_interruptible(&dev->bulk_in_completion);+rv = wait_event_interruptible(dev->bulk_in_wait, (!dev->ongoing_read)); if (rv < 0) goto exit;-/*- * by waiting we also semiprocessed the urb- * we must finish now- */-dev->bulk_in_copied = 0;-dev->processed_urb = 1;-}--if (!dev->processed_urb) {-/*- * the URB hasn't been processed- * do it now- */-wait_for_completion(&dev->bulk_in_completion);-dev->bulk_in_copied = 0;-dev->processed_urb = 1; }  /* errors must be reported */@@ -289,8 +275,6 @@ retry: dev->errors = 0; /* to preserve notifications about reset */ rv = (rv == -EPIPE) ? rv : -EIO;-/* no data to deliver */-dev->bulk_in_filled = 0; /* report it */ goto exit; }@@ -526,7 +510,7 @@ static int skel_probe(struct usb_interface *interface, mutex_init(&dev->io_mutex); spin_lock_init(&dev->err_lock); init_usb_anchor(&dev->submitted);-init_completion(&dev->bulk_in_completion);+init_waitqueue_head(&dev->bulk_in_wait);  dev->udev = usb_get_dev(interface_to_usbdev(interface)); dev->interface = interface;