usb: Introduce Xen pvUSB frontend (xen hcd)

Introduces the Xen pvUSB frontend. With pvUSB it is possible for a Xen
domU to communicate with a USB device assigned to that domU. The
communication is all done via the pvUSB backend in a driver domain
(usually Dom0) which is owner of the physical device.

The pvUSB frontend is a USB hcd for a virtual USB host connector.

The code is taken from the pvUSB implementation in Xen done by Fujitsu
based on Linux kernel 2.6.18.

Changes from the original version are:
- port to upstream kernel
- put all code in just one source file
- move module to appropriate location in kernel tree
- adapt to Linux style guide
- minor code modifications to increase readability
Signed-off-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20211123132048.5335-3-jgross@suse.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/Kconfig

@@ -772,3 +772,14 @@ config USB_HCD_TEST_MODE
 	  This option is of interest only to developers who need to validate
 	  their USB hardware designs.  It is not needed for normal use.  If
 	  unsure, say N.
+
+config USB_XEN_HCD
+	tristate "Xen usb virtual host driver"
+	depends on XEN
+	select XEN_XENBUS_FRONTEND
+	help
+	  The Xen usb virtual host driver serves as a frontend driver enabling
+	  a Xen guest system to access USB Devices passed through to the guest
+	  by the Xen host (usually Dom0).
+	  Only needed if the kernel is running in a Xen guest and generic
+	  access to a USB device is needed.

drivers/usb/host/Makefile

@@ -85,3 +85,4 @@ obj-$(CONFIG_USB_HCD_BCMA)	+= bcma-hcd.o
 obj-$(CONFIG_USB_HCD_SSB)	+= ssb-hcd.o
 obj-$(CONFIG_USB_FOTG210_HCD)	+= fotg210-hcd.o
 obj-$(CONFIG_USB_MAX3421_HCD)	+= max3421-hcd.o
+obj-$(CONFIG_USB_XEN_HCD)	+= xen-hcd.o

drivers/usb/host/xen-hcd.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * xen-hcd.c
+ *
+ * Xen USB Virtual Host Controller driver
+ *
+ * Copyright (C) 2009, FUJITSU LABORATORIES LTD.
+ * Author: Noboru Iwamatsu <n_iwamatsu@jp.fujitsu.com>
+ */
+
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/list.h>
+#include <linux/usb/hcd.h>
+#include <linux/io.h>
+
+#include <xen/xen.h>
+#include <xen/xenbus.h>
+#include <xen/grant_table.h>
+#include <xen/events.h>
+#include <xen/page.h>
+
+#include <xen/interface/io/usbif.h>
+
+/* Private per-URB data */
+struct urb_priv {
+	struct list_head list;
+	struct urb *urb;
+	int req_id;		/* RING_REQUEST id for submitting */
+	int unlink_req_id;	/* RING_REQUEST id for unlinking */
+	int status;
+	bool unlinked;		/* dequeued marker */
+};
+
+/* virtual roothub port status */
+struct rhport_status {
+	__u32 status;
+	bool resuming;		/* in resuming */
+	bool c_connection;	/* connection changed */
+	unsigned long timeout;
+};
+
+/* status of attached device */
+struct vdevice_status {
+	int devnum;
+	enum usb_device_state status;
+	enum usb_device_speed speed;
+};
+
+/* RING request shadow */
+struct usb_shadow {
+	struct xenusb_urb_request req;
+	struct urb *urb;
+};
+
+struct xenhcd_info {
+	/* Virtual Host Controller has 4 urb queues */
+	struct list_head pending_submit_list;
+	struct list_head pending_unlink_list;
+	struct list_head in_progress_list;
+	struct list_head giveback_waiting_list;
+
+	spinlock_t lock;
+
+	/* timer that kick pending and giveback waiting urbs */
+	struct timer_list watchdog;
+	unsigned long actions;
+
+	/* virtual root hub */
+	int rh_numports;
+	struct rhport_status ports[XENUSB_MAX_PORTNR];
+	struct vdevice_status devices[XENUSB_MAX_PORTNR];
+
+	/* Xen related staff */
+	struct xenbus_device *xbdev;
+	int urb_ring_ref;
+	int conn_ring_ref;
+	struct xenusb_urb_front_ring urb_ring;
+	struct xenusb_conn_front_ring conn_ring;
+
+	unsigned int evtchn;
+	unsigned int irq;
+	struct usb_shadow shadow[XENUSB_URB_RING_SIZE];
+	unsigned int shadow_free;
+
+	bool error;
+};
+
+#define GRANT_INVALID_REF 0
+
+#define XENHCD_RING_JIFFIES (HZ/200)
+#define XENHCD_SCAN_JIFFIES 1
+
+enum xenhcd_timer_action {
+	TIMER_RING_WATCHDOG,
+	TIMER_SCAN_PENDING_URBS,
+};
+
+static struct kmem_cache *xenhcd_urbp_cachep;
+
+static inline struct xenhcd_info *xenhcd_hcd_to_info(struct usb_hcd *hcd)
+{
+	return (struct xenhcd_info *)hcd->hcd_priv;
+}
+
+static inline struct usb_hcd *xenhcd_info_to_hcd(struct xenhcd_info *info)
+{
+	return container_of((void *)info, struct usb_hcd, hcd_priv);
+}
+
+static void xenhcd_set_error(struct xenhcd_info *info, const char *msg)
+{
+	info->error = true;
+
+	pr_alert("xen-hcd: protocol error: %s!\n", msg);
+}
+
+static inline void xenhcd_timer_action_done(struct xenhcd_info *info,
+					    enum xenhcd_timer_action action)
+{
+	clear_bit(action, &info->actions);
+}
+
+static void xenhcd_timer_action(struct xenhcd_info *info,
+				enum xenhcd_timer_action action)
+{
+	if (timer_pending(&info->watchdog) &&
+	    test_bit(TIMER_SCAN_PENDING_URBS, &info->actions))
+		return;
+
+	if (!test_and_set_bit(action, &info->actions)) {
+		unsigned long t;
+
+		switch (action) {
+		case TIMER_RING_WATCHDOG:
+			t = XENHCD_RING_JIFFIES;
+			break;
+		default:
+			t = XENHCD_SCAN_JIFFIES;
+			break;
+		}
+		mod_timer(&info->watchdog, t + jiffies);
+	}
+}
+
+/*
+ * set virtual port connection status
+ */
+static void xenhcd_set_connect_state(struct xenhcd_info *info, int portnum)
+{
+	int port;
+
+	port = portnum - 1;
+	if (info->ports[port].status & USB_PORT_STAT_POWER) {
+		switch (info->devices[port].speed) {
+		case XENUSB_SPEED_NONE:
+			info->ports[port].status &=
+				~(USB_PORT_STAT_CONNECTION |
+				  USB_PORT_STAT_ENABLE |
+				  USB_PORT_STAT_LOW_SPEED |
+				  USB_PORT_STAT_HIGH_SPEED |
+				  USB_PORT_STAT_SUSPEND);
+			break;
+		case XENUSB_SPEED_LOW:
+			info->ports[port].status |= USB_PORT_STAT_CONNECTION;
+			info->ports[port].status |= USB_PORT_STAT_LOW_SPEED;
+			break;
+		case XENUSB_SPEED_FULL:
+			info->ports[port].status |= USB_PORT_STAT_CONNECTION;
+			break;
+		case XENUSB_SPEED_HIGH:
+			info->ports[port].status |= USB_PORT_STAT_CONNECTION;
+			info->ports[port].status |= USB_PORT_STAT_HIGH_SPEED;
+			break;
+		default: /* error */
+			return;
+		}
+		info->ports[port].status |= (USB_PORT_STAT_C_CONNECTION << 16);
+	}
+}
+
+/*
+ * set virtual device connection status
+ */
+static int xenhcd_rhport_connect(struct xenhcd_info *info, __u8 portnum,
+				 __u8 speed)
+{
+	int port;
+
+	if (portnum < 1 || portnum > info->rh_numports)
+		return -EINVAL; /* invalid port number */
+
+	port = portnum - 1;
+	if (info->devices[port].speed != speed) {
+		switch (speed) {
+		case XENUSB_SPEED_NONE: /* disconnect */
+			info->devices[port].status = USB_STATE_NOTATTACHED;
+			break;
+		case XENUSB_SPEED_LOW:
+		case XENUSB_SPEED_FULL:
+		case XENUSB_SPEED_HIGH:
+			info->devices[port].status = USB_STATE_ATTACHED;
+			break;
+		default: /* error */
+			return -EINVAL;
+		}
+		info->devices[port].speed = speed;
+		info->ports[port].c_connection = true;
+
+		xenhcd_set_connect_state(info, portnum);
+	}
+
+	return 0;
+}
+
+/*
+ * SetPortFeature(PORT_SUSPENDED)
+ */
+static void xenhcd_rhport_suspend(struct xenhcd_info *info, int portnum)
+{
+	int port;
+
+	port = portnum - 1;
+	info->ports[port].status |= USB_PORT_STAT_SUSPEND;
+	info->devices[port].status = USB_STATE_SUSPENDED;
+}
+
+/*
+ * ClearPortFeature(PORT_SUSPENDED)
+ */
+static void xenhcd_rhport_resume(struct xenhcd_info *info, int portnum)
+{
+	int port;
+
+	port = portnum - 1;
+	if (info->ports[port].status & USB_PORT_STAT_SUSPEND) {
+		info->ports[port].resuming = true;
+		info->ports[port].timeout = jiffies + msecs_to_jiffies(20);
+	}
+}
+
+/*
+ * SetPortFeature(PORT_POWER)
+ */
+static void xenhcd_rhport_power_on(struct xenhcd_info *info, int portnum)
+{
+	int port;
+
+	port = portnum - 1;
+	if ((info->ports[port].status & USB_PORT_STAT_POWER) == 0) {
+		info->ports[port].status |= USB_PORT_STAT_POWER;
+		if (info->devices[port].status != USB_STATE_NOTATTACHED)
+			info->devices[port].status = USB_STATE_POWERED;
+		if (info->ports[port].c_connection)
+			xenhcd_set_connect_state(info, portnum);
+	}
+}
+
+/*
+ * ClearPortFeature(PORT_POWER)
+ * SetConfiguration(non-zero)
+ * Power_Source_Off
+ * Over-current
+ */
+static void xenhcd_rhport_power_off(struct xenhcd_info *info, int portnum)
+{
+	int port;
+
+	port = portnum - 1;
+	if (info->ports[port].status & USB_PORT_STAT_POWER) {
+		info->ports[port].status = 0;
+		if (info->devices[port].status != USB_STATE_NOTATTACHED)
+			info->devices[port].status = USB_STATE_ATTACHED;
+	}
+}
+
+/*
+ * ClearPortFeature(PORT_ENABLE)
+ */
+static void xenhcd_rhport_disable(struct xenhcd_info *info, int portnum)
+{
+	int port;
+
+	port = portnum - 1;
+	info->ports[port].status &= ~USB_PORT_STAT_ENABLE;
+	info->ports[port].status &= ~USB_PORT_STAT_SUSPEND;
+	info->ports[port].resuming = false;
+	if (info->devices[port].status != USB_STATE_NOTATTACHED)
+		info->devices[port].status = USB_STATE_POWERED;
+}
+
+/*
+ * SetPortFeature(PORT_RESET)
+ */
+static void xenhcd_rhport_reset(struct xenhcd_info *info, int portnum)
+{
+	int port;
+
+	port = portnum - 1;
+	info->ports[port].status &= ~(USB_PORT_STAT_ENABLE |
+				      USB_PORT_STAT_LOW_SPEED |
+				      USB_PORT_STAT_HIGH_SPEED);
+	info->ports[port].status |= USB_PORT_STAT_RESET;
+
+	if (info->devices[port].status != USB_STATE_NOTATTACHED)
+		info->devices[port].status = USB_STATE_ATTACHED;
+
+	/* 10msec reset signaling */
+	info->ports[port].timeout = jiffies + msecs_to_jiffies(10);
+}
+
+#ifdef CONFIG_PM
+static int xenhcd_bus_suspend(struct usb_hcd *hcd)
+{
+	struct xenhcd_info *info = xenhcd_hcd_to_info(hcd);
+	int ret = 0;
+	int i, ports;
+
+	ports = info->rh_numports;
+
+	spin_lock_irq(&info->lock);
+	if (!test_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags)) {
+		ret = -ESHUTDOWN;
+	} else {
+		/* suspend any active ports*/
+		for (i = 1; i <= ports; i++)
+			xenhcd_rhport_suspend(info, i);
+	}
+	spin_unlock_irq(&info->lock);
+
+	del_timer_sync(&info->watchdog);
+
+	return ret;
+}
+
+static int xenhcd_bus_resume(struct usb_hcd *hcd)
+{
+	struct xenhcd_info *info = xenhcd_hcd_to_info(hcd);
+	int ret = 0;
+	int i, ports;
+
+	ports = info->rh_numports;
+
+	spin_lock_irq(&info->lock);
+	if (!test_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags)) {
+		ret = -ESHUTDOWN;
+	} else {
+		/* resume any suspended ports*/
+		for (i = 1; i <= ports; i++)
+			xenhcd_rhport_resume(info, i);
+	}
+	spin_unlock_irq(&info->lock);
+
+	return ret;
+}
+#endif
+
+static void xenhcd_hub_descriptor(struct xenhcd_info *info,
+				  struct usb_hub_descriptor *desc)
+{
+	__u16 temp;
+	int ports = info->rh_numports;
+
+	desc->bDescriptorType = 0x29;
+	desc->bPwrOn2PwrGood = 10; /* EHCI says 20ms max */
+	desc->bHubContrCurrent = 0;
+	desc->bNbrPorts = ports;
+
+	/* size of DeviceRemovable and PortPwrCtrlMask fields */
+	temp = 1 + (ports / 8);
+	desc->bDescLength = 7 + 2 * temp;
+
+	/* bitmaps for DeviceRemovable and PortPwrCtrlMask */
+	memset(&desc->u.hs.DeviceRemovable[0], 0, temp);
+	memset(&desc->u.hs.DeviceRemovable[temp], 0xff, temp);
+
+	/* per-port over current reporting and no power switching */
+	temp = 0x000a;
+	desc->wHubCharacteristics = cpu_to_le16(temp);
+}
+
+/* port status change mask for hub_status_data */
+#define PORT_C_MASK	((USB_PORT_STAT_C_CONNECTION |		\
+			  USB_PORT_STAT_C_ENABLE |		\
+			  USB_PORT_STAT_C_SUSPEND |		\
+			  USB_PORT_STAT_C_OVERCURRENT |		\
+			  USB_PORT_STAT_C_RESET) << 16)
+
+/*
+ * See USB 2.0 Spec, 11.12.4 Hub and Port Status Change Bitmap.
+ * If port status changed, writes the bitmap to buf and return
+ * that length(number of bytes).
+ * If Nothing changed, return 0.
+ */
+static int xenhcd_hub_status_data(struct usb_hcd *hcd, char *buf)
+{
+	struct xenhcd_info *info = xenhcd_hcd_to_info(hcd);
+	int ports;
+	int i;
+	unsigned long flags;
+	int ret;
+	int changed = 0;
+
+	/* initialize the status to no-changes */
+	ports = info->rh_numports;
+	ret = 1 + (ports / 8);
+	memset(buf, 0, ret);
+
+	spin_lock_irqsave(&info->lock, flags);
+
+	for (i = 0; i < ports; i++) {
+		/* check status for each port */
+		if (info->ports[i].status & PORT_C_MASK) {
+			buf[(i + 1) / 8] |= 1 << (i + 1) % 8;
+			changed = 1;
+		}
+	}
+
+	if ((hcd->state == HC_STATE_SUSPENDED) && (changed == 1))
+		usb_hcd_resume_root_hub(hcd);
+
+	spin_unlock_irqrestore(&info->lock, flags);
+
+	return changed ? ret : 0;
+}
+
+static int xenhcd_hub_control(struct usb_hcd *hcd, __u16 typeReq, __u16 wValue,
+			      __u16 wIndex, char *buf, __u16 wLength)
+{
+	struct xenhcd_info *info = xenhcd_hcd_to_info(hcd);
+	int ports = info->rh_numports;
+	unsigned long flags;
+	int ret = 0;
+	int i;
+	int changed = 0;
+
+	spin_lock_irqsave(&info->lock, flags);
+	switch (typeReq) {
+	case ClearHubFeature:
+		/* ignore this request */
+		break;
+	case ClearPortFeature:
+		if (!wIndex || wIndex > ports)
+			goto error;
+
+		switch (wValue) {
+		case USB_PORT_FEAT_SUSPEND:
+			xenhcd_rhport_resume(info, wIndex);
+			break;
+		case USB_PORT_FEAT_POWER:
+			xenhcd_rhport_power_off(info, wIndex);
+			break;
+		case USB_PORT_FEAT_ENABLE:
+			xenhcd_rhport_disable(info, wIndex);
+			break;
+		case USB_PORT_FEAT_C_CONNECTION:
+			info->ports[wIndex - 1].c_connection = false;
+			fallthrough;
+		default:
+			info->ports[wIndex - 1].status &= ~(1 << wValue);
+			break;
+		}
+		break;
+	case GetHubDescriptor:
+		xenhcd_hub_descriptor(info, (struct usb_hub_descriptor *)buf);
+		break;
+	case GetHubStatus:
+		/* always local power supply good and no over-current exists. */
+		*(__le32 *)buf = cpu_to_le32(0);
+		break;
+	case GetPortStatus:
+		if (!wIndex || wIndex > ports)
+			goto error;
+
+		wIndex--;
+
+		/* resume completion */
+		if (info->ports[wIndex].resuming &&
+		    time_after_eq(jiffies, info->ports[wIndex].timeout)) {
+			info->ports[wIndex].status |=
+				USB_PORT_STAT_C_SUSPEND << 16;
+			info->ports[wIndex].status &= ~USB_PORT_STAT_SUSPEND;
+		}
+
+		/* reset completion */
+		if ((info->ports[wIndex].status & USB_PORT_STAT_RESET) != 0 &&
+		    time_after_eq(jiffies, info->ports[wIndex].timeout)) {
+			info->ports[wIndex].status |=
+				USB_PORT_STAT_C_RESET << 16;
+			info->ports[wIndex].status &= ~USB_PORT_STAT_RESET;
+
+			if (info->devices[wIndex].status !=
+			    USB_STATE_NOTATTACHED) {
+				info->ports[wIndex].status |=
+					USB_PORT_STAT_ENABLE;
+				info->devices[wIndex].status =
+					USB_STATE_DEFAULT;
+			}
+
+			switch (info->devices[wIndex].speed) {
+			case XENUSB_SPEED_LOW:
+				info->ports[wIndex].status |=
+					USB_PORT_STAT_LOW_SPEED;
+				break;
+			case XENUSB_SPEED_HIGH:
+				info->ports[wIndex].status |=
+					USB_PORT_STAT_HIGH_SPEED;
+				break;
+			default:
+				break;
+			}
+		}
+
+		*(__le32 *)buf = cpu_to_le32(info->ports[wIndex].status);
+		break;
+	case SetPortFeature:
+		if (!wIndex || wIndex > ports)
+			goto error;
+
+		switch (wValue) {
+		case USB_PORT_FEAT_POWER:
+			xenhcd_rhport_power_on(info, wIndex);
+			break;
+		case USB_PORT_FEAT_RESET:
+			xenhcd_rhport_reset(info, wIndex);
+			break;
+		case USB_PORT_FEAT_SUSPEND:
+			xenhcd_rhport_suspend(info, wIndex);
+			break;
+		default:
+			if (info->ports[wIndex-1].status & USB_PORT_STAT_POWER)
+				info->ports[wIndex-1].status |= (1 << wValue);
+		}
+		break;
+
+	case SetHubFeature:
+		/* not supported */
+	default:
+error:
+		ret = -EPIPE;
+	}
+	spin_unlock_irqrestore(&info->lock, flags);
+
+	/* check status for each port */
+	for (i = 0; i < ports; i++) {
+		if (info->ports[i].status & PORT_C_MASK)
+			changed = 1;
+	}
+	if (changed)
+		usb_hcd_poll_rh_status(hcd);
+
+	return ret;
+}
+
+static void xenhcd_free_urb_priv(struct urb_priv *urbp)
+{
+	urbp->urb->hcpriv = NULL;
+	kmem_cache_free(xenhcd_urbp_cachep, urbp);
+}
+
+static inline unsigned int xenhcd_get_id_from_freelist(struct xenhcd_info *info)
+{
+	unsigned int free;
+
+	free = info->shadow_free;
+	info->shadow_free = info->shadow[free].req.id;
+	info->shadow[free].req.id = 0x0fff; /* debug */
+	return free;
+}
+
+static inline void xenhcd_add_id_to_freelist(struct xenhcd_info *info,
+					     unsigned int id)
+{
+	info->shadow[id].req.id	= info->shadow_free;
+	info->shadow[id].urb = NULL;
+	info->shadow_free = id;
+}
+
+static inline int xenhcd_count_pages(void *addr, int length)
+{
+	unsigned long vaddr = (unsigned long)addr;
+
+	return PFN_UP(vaddr + length) - PFN_DOWN(vaddr);
+}
+
+static void xenhcd_gnttab_map(struct xenhcd_info *info, void *addr, int length,
+			      grant_ref_t *gref_head,
+			      struct xenusb_request_segment *seg,
+			      int nr_pages, int flags)
+{
+	grant_ref_t ref;
+	unsigned long buffer_mfn;
+	unsigned int offset;
+	unsigned int len = length;
+	unsigned int bytes;
+	int i;
+
+	for (i = 0; i < nr_pages; i++) {
+		buffer_mfn = PFN_DOWN(arbitrary_virt_to_machine(addr).maddr);
+		offset = offset_in_page(addr);
+
+		bytes = PAGE_SIZE - offset;
+		if (bytes > len)
+			bytes = len;
+
+		ref = gnttab_claim_grant_reference(gref_head);
+		gnttab_grant_foreign_access_ref(ref, info->xbdev->otherend_id,
+						buffer_mfn, flags);
+		seg[i].gref = ref;
+		seg[i].offset = (__u16)offset;
+		seg[i].length = (__u16)bytes;
+
+		addr += bytes;
+		len -= bytes;
+	}
+}
+
+static __u32 xenhcd_pipe_urb_to_xenusb(__u32 urb_pipe, __u8 port)
+{
+	static __u32 pipe;
+
+	pipe = usb_pipedevice(urb_pipe) << XENUSB_PIPE_DEV_SHIFT;
+	pipe |= usb_pipeendpoint(urb_pipe) << XENUSB_PIPE_EP_SHIFT;
+	if (usb_pipein(urb_pipe))
+		pipe |= XENUSB_PIPE_DIR;
+	switch (usb_pipetype(urb_pipe)) {
+	case PIPE_ISOCHRONOUS:
+		pipe |= XENUSB_PIPE_TYPE_ISOC << XENUSB_PIPE_TYPE_SHIFT;
+		break;
+	case PIPE_INTERRUPT:
+		pipe |= XENUSB_PIPE_TYPE_INT << XENUSB_PIPE_TYPE_SHIFT;
+		break;
+	case PIPE_CONTROL:
+		pipe |= XENUSB_PIPE_TYPE_CTRL << XENUSB_PIPE_TYPE_SHIFT;
+		break;
+	case PIPE_BULK:
+		pipe |= XENUSB_PIPE_TYPE_BULK << XENUSB_PIPE_TYPE_SHIFT;
+		break;
+	}
+	pipe = xenusb_setportnum_pipe(pipe, port);
+
+	return pipe;
+}
+
+static int xenhcd_map_urb_for_request(struct xenhcd_info *info, struct urb *urb,
+				      struct xenusb_urb_request *req)
+{
+	grant_ref_t gref_head;
+	int nr_buff_pages = 0;
+	int nr_isodesc_pages = 0;
+	int nr_grants = 0;
+
+	if (urb->transfer_buffer_length) {
+		nr_buff_pages = xenhcd_count_pages(urb->transfer_buffer,
+						urb->transfer_buffer_length);
+
+		if (usb_pipeisoc(urb->pipe))
+			nr_isodesc_pages = xenhcd_count_pages(
+				&urb->iso_frame_desc[0],
+				sizeof(struct usb_iso_packet_descriptor) *
+				urb->number_of_packets);
+
+		nr_grants = nr_buff_pages + nr_isodesc_pages;
+		if (nr_grants > XENUSB_MAX_SEGMENTS_PER_REQUEST) {
+			pr_err("xenhcd: error: %d grants\n", nr_grants);
+			return -E2BIG;
+		}
+
+		if (gnttab_alloc_grant_references(nr_grants, &gref_head)) {
+			pr_err("xenhcd: gnttab_alloc_grant_references() error\n");
+			return -ENOMEM;
+		}
+
+		xenhcd_gnttab_map(info, urb->transfer_buffer,
+				  urb->transfer_buffer_length, &gref_head,
+				  &req->seg[0], nr_buff_pages,
+				  usb_pipein(urb->pipe) ? 0 : GTF_readonly);
+	}
+
+	req->pipe = xenhcd_pipe_urb_to_xenusb(urb->pipe, urb->dev->portnum);
+	req->transfer_flags = 0;
+	if (urb->transfer_flags & URB_SHORT_NOT_OK)
+		req->transfer_flags |= XENUSB_SHORT_NOT_OK;
+	req->buffer_length = urb->transfer_buffer_length;
+	req->nr_buffer_segs = nr_buff_pages;
+
+	switch (usb_pipetype(urb->pipe)) {
+	case PIPE_ISOCHRONOUS:
+		req->u.isoc.interval = urb->interval;
+		req->u.isoc.start_frame = urb->start_frame;
+		req->u.isoc.number_of_packets = urb->number_of_packets;
+		req->u.isoc.nr_frame_desc_segs = nr_isodesc_pages;
+
+		xenhcd_gnttab_map(info, &urb->iso_frame_desc[0],
+				  sizeof(struct usb_iso_packet_descriptor) *
+				  urb->number_of_packets,
+				  &gref_head, &req->seg[nr_buff_pages],
+				  nr_isodesc_pages, 0);
+		break;
+	case PIPE_INTERRUPT:
+		req->u.intr.interval = urb->interval;
+		break;
+	case PIPE_CONTROL:
+		if (urb->setup_packet)
+			memcpy(req->u.ctrl, urb->setup_packet, 8);
+		break;
+	case PIPE_BULK:
+		break;
+	default:
+		break;
+	}
+
+	if (nr_grants)
+		gnttab_free_grant_references(gref_head);
+
+	return 0;
+}
+
+static void xenhcd_gnttab_done(struct usb_shadow *shadow)
+{
+	int nr_segs = 0;
+	int i;
+
+	nr_segs = shadow->req.nr_buffer_segs;
+
+	if (xenusb_pipeisoc(shadow->req.pipe))
+		nr_segs += shadow->req.u.isoc.nr_frame_desc_segs;
+
+	for (i = 0; i < nr_segs; i++)
+		gnttab_end_foreign_access(shadow->req.seg[i].gref, 0, 0UL);
+
+	shadow->req.nr_buffer_segs = 0;
+	shadow->req.u.isoc.nr_frame_desc_segs = 0;
+}
+
+static int xenhcd_translate_status(int status)
+{
+	switch (status) {
+	case XENUSB_STATUS_OK:
+		return 0;
+	case XENUSB_STATUS_NODEV:
+		return -ENODEV;
+	case XENUSB_STATUS_INVAL:
+		return -EINVAL;
+	case XENUSB_STATUS_STALL:
+		return -EPIPE;
+	case XENUSB_STATUS_IOERROR:
+		return -EPROTO;
+	case XENUSB_STATUS_BABBLE:
+		return -EOVERFLOW;
+	default:
+		return -ESHUTDOWN;
+	}
+}
+
+static void xenhcd_giveback_urb(struct xenhcd_info *info, struct urb *urb,
+				int status)
+{
+	struct urb_priv *urbp = (struct urb_priv *)urb->hcpriv;
+	int priv_status = urbp->status;
+
+	list_del_init(&urbp->list);
+	xenhcd_free_urb_priv(urbp);
+
+	if (urb->status == -EINPROGRESS)
+		urb->status = xenhcd_translate_status(status);
+
+	spin_unlock(&info->lock);
+	usb_hcd_giveback_urb(xenhcd_info_to_hcd(info), urb,
+			     priv_status <= 0 ? priv_status : urb->status);
+	spin_lock(&info->lock);
+}
+
+static int xenhcd_do_request(struct xenhcd_info *info, struct urb_priv *urbp)
+{
+	struct xenusb_urb_request *req;
+	struct urb *urb = urbp->urb;
+	unsigned int id;
+	int notify;
+	int ret;
+
+	id = xenhcd_get_id_from_freelist(info);
+	req = &info->shadow[id].req;
+	req->id = id;
+
+	if (unlikely(urbp->unlinked)) {
+		req->u.unlink.unlink_id = urbp->req_id;
+		req->pipe = xenusb_setunlink_pipe(xenhcd_pipe_urb_to_xenusb(
+						 urb->pipe, urb->dev->portnum));
+		urbp->unlink_req_id = id;
+	} else {
+		ret = xenhcd_map_urb_for_request(info, urb, req);
+		if (ret) {
+			xenhcd_add_id_to_freelist(info, id);
+			return ret;
+		}
+		urbp->req_id = id;
+	}
+
+	req = RING_GET_REQUEST(&info->urb_ring, info->urb_ring.req_prod_pvt);
+	*req = info->shadow[id].req;
+
+	info->urb_ring.req_prod_pvt++;
+	info->shadow[id].urb = urb;
+
+	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&info->urb_ring, notify);
+	if (notify)
+		notify_remote_via_irq(info->irq);
+
+	return 0;
+}
+
+static void xenhcd_kick_pending_urbs(struct xenhcd_info *info)
+{
+	struct urb_priv *urbp;
+
+	while (!list_empty(&info->pending_submit_list)) {
+		if (RING_FULL(&info->urb_ring)) {
+			xenhcd_timer_action(info, TIMER_RING_WATCHDOG);
+			return;
+		}
+
+		urbp = list_entry(info->pending_submit_list.next,
+				  struct urb_priv, list);
+		if (!xenhcd_do_request(info, urbp))
+			list_move_tail(&urbp->list, &info->in_progress_list);
+		else
+			xenhcd_giveback_urb(info, urbp->urb, -ESHUTDOWN);
+	}
+	xenhcd_timer_action_done(info, TIMER_SCAN_PENDING_URBS);
+}
+
+/*
+ * caller must lock info->lock
+ */
+static void xenhcd_cancel_all_enqueued_urbs(struct xenhcd_info *info)
+{
+	struct urb_priv *urbp, *tmp;
+	int req_id;
+
+	list_for_each_entry_safe(urbp, tmp, &info->in_progress_list, list) {
+		req_id = urbp->req_id;
+		if (!urbp->unlinked) {
+			xenhcd_gnttab_done(&info->shadow[req_id]);
+			if (urbp->urb->status == -EINPROGRESS)
+				/* not dequeued */
+				xenhcd_giveback_urb(info, urbp->urb,
+						    -ESHUTDOWN);
+			else	/* dequeued */
+				xenhcd_giveback_urb(info, urbp->urb,
+						    urbp->urb->status);
+		}
+		info->shadow[req_id].urb = NULL;
+	}
+
+	list_for_each_entry_safe(urbp, tmp, &info->pending_submit_list, list)
+		xenhcd_giveback_urb(info, urbp->urb, -ESHUTDOWN);
+}
+
+/*
+ * caller must lock info->lock
+ */
+static void xenhcd_giveback_unlinked_urbs(struct xenhcd_info *info)
+{
+	struct urb_priv *urbp, *tmp;
+
+	list_for_each_entry_safe(urbp, tmp, &info->giveback_waiting_list, list)
+		xenhcd_giveback_urb(info, urbp->urb, urbp->urb->status);
+}
+
+static int xenhcd_submit_urb(struct xenhcd_info *info, struct urb_priv *urbp)
+{
+	int ret;
+
+	if (RING_FULL(&info->urb_ring)) {
+		list_add_tail(&urbp->list, &info->pending_submit_list);
+		xenhcd_timer_action(info, TIMER_RING_WATCHDOG);
+		return 0;
+	}
+
+	if (!list_empty(&info->pending_submit_list)) {
+		list_add_tail(&urbp->list, &info->pending_submit_list);
+		xenhcd_timer_action(info, TIMER_SCAN_PENDING_URBS);
+		return 0;
+	}
+
+	ret = xenhcd_do_request(info, urbp);
+	if (ret == 0)
+		list_add_tail(&urbp->list, &info->in_progress_list);
+
+	return ret;
+}
+
+static int xenhcd_unlink_urb(struct xenhcd_info *info, struct urb_priv *urbp)
+{
+	int ret;
+
+	/* already unlinked? */
+	if (urbp->unlinked)
+		return -EBUSY;
+
+	urbp->unlinked = true;
+
+	/* the urb is still in pending_submit queue */
+	if (urbp->req_id == ~0) {
+		list_move_tail(&urbp->list, &info->giveback_waiting_list);
+		xenhcd_timer_action(info, TIMER_SCAN_PENDING_URBS);
+		return 0;
+	}
+
+	/* send unlink request to backend */
+	if (RING_FULL(&info->urb_ring)) {
+		list_move_tail(&urbp->list, &info->pending_unlink_list);
+		xenhcd_timer_action(info, TIMER_RING_WATCHDOG);
+		return 0;
+	}
+
+	if (!list_empty(&info->pending_unlink_list)) {
+		list_move_tail(&urbp->list, &info->pending_unlink_list);
+		xenhcd_timer_action(info, TIMER_SCAN_PENDING_URBS);
+		return 0;
+	}
+
+	ret = xenhcd_do_request(info, urbp);
+	if (ret == 0)
+		list_move_tail(&urbp->list, &info->in_progress_list);
+
+	return ret;
+}
+
+static int xenhcd_urb_request_done(struct xenhcd_info *info)
+{
+	struct xenusb_urb_response res;
+	struct urb *urb;
+	RING_IDX i, rp;
+	__u16 id;
+	int more_to_do = 0;
+	unsigned long flags;
+
+	spin_lock_irqsave(&info->lock, flags);
+
+	rp = info->urb_ring.sring->rsp_prod;
+	if (RING_RESPONSE_PROD_OVERFLOW(&info->urb_ring, rp)) {
+		xenhcd_set_error(info, "Illegal index on urb-ring");
+		return 0;
+	}
+	rmb(); /* ensure we see queued responses up to "rp" */
+
+	for (i = info->urb_ring.rsp_cons; i != rp; i++) {
+		RING_COPY_RESPONSE(&info->urb_ring, i, &res);
+		id = res.id;
+		if (id >= XENUSB_URB_RING_SIZE) {
+			xenhcd_set_error(info, "Illegal data on urb-ring");
+			continue;
+		}
+
+		if (likely(xenusb_pipesubmit(info->shadow[id].req.pipe))) {
+			xenhcd_gnttab_done(&info->shadow[id]);
+			urb = info->shadow[id].urb;
+			if (likely(urb)) {
+				urb->actual_length = res.actual_length;
+				urb->error_count = res.error_count;
+				urb->start_frame = res.start_frame;
+				xenhcd_giveback_urb(info, urb, res.status);
+			}
+		}
+
+		xenhcd_add_id_to_freelist(info, id);
+	}
+	info->urb_ring.rsp_cons = i;
+
+	if (i != info->urb_ring.req_prod_pvt)
+		RING_FINAL_CHECK_FOR_RESPONSES(&info->urb_ring, more_to_do);
+	else
+		info->urb_ring.sring->rsp_event = i + 1;
+
+	spin_unlock_irqrestore(&info->lock, flags);
+
+	return more_to_do;
+}
+
+static int xenhcd_conn_notify(struct xenhcd_info *info)
+{
+	struct xenusb_conn_response res;
+	struct xenusb_conn_request *req;
+	RING_IDX rc, rp;
+	__u16 id;
+	__u8 portnum, speed;
+	int more_to_do = 0;
+	int notify;
+	int port_changed = 0;
+	unsigned long flags;
+
+	spin_lock_irqsave(&info->lock, flags);
+
+	rc = info->conn_ring.rsp_cons;
+	rp = info->conn_ring.sring->rsp_prod;
+	if (RING_RESPONSE_PROD_OVERFLOW(&info->conn_ring, rp)) {
+		xenhcd_set_error(info, "Illegal index on conn-ring");
+		return 0;
+	}
+	rmb(); /* ensure we see queued responses up to "rp" */
+
+	while (rc != rp) {
+		RING_COPY_RESPONSE(&info->conn_ring, rc, &res);
+		id = res.id;
+		portnum = res.portnum;
+		speed = res.speed;
+		info->conn_ring.rsp_cons = ++rc;
+
+		if (xenhcd_rhport_connect(info, portnum, speed)) {
+			xenhcd_set_error(info, "Illegal data on conn-ring");
+			return 0;
+		}
+
+		if (info->ports[portnum - 1].c_connection)
+			port_changed = 1;
+
+		barrier();
+
+		req = RING_GET_REQUEST(&info->conn_ring,
+				       info->conn_ring.req_prod_pvt);
+		req->id = id;
+		info->conn_ring.req_prod_pvt++;
+	}
+
+	if (rc != info->conn_ring.req_prod_pvt)
+		RING_FINAL_CHECK_FOR_RESPONSES(&info->conn_ring, more_to_do);
+	else
+		info->conn_ring.sring->rsp_event = rc + 1;
+
+	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&info->conn_ring, notify);
+	if (notify)
+		notify_remote_via_irq(info->irq);
+
+	spin_unlock_irqrestore(&info->lock, flags);
+
+	if (port_changed)
+		usb_hcd_poll_rh_status(xenhcd_info_to_hcd(info));
+
+	return more_to_do;
+}
+
+static irqreturn_t xenhcd_int(int irq, void *dev_id)
+{
+	struct xenhcd_info *info = (struct xenhcd_info *)dev_id;
+
+	if (unlikely(info->error))
+		return IRQ_HANDLED;
+
+	while (xenhcd_urb_request_done(info) | xenhcd_conn_notify(info))
+		/* Yield point for this unbounded loop. */
+		cond_resched();
+
+	return IRQ_HANDLED;
+}
+
+static void xenhcd_destroy_rings(struct xenhcd_info *info)
+{
+	if (info->irq)
+		unbind_from_irqhandler(info->irq, info);
+	info->irq = 0;
+
+	if (info->urb_ring_ref != GRANT_INVALID_REF) {
+		gnttab_end_foreign_access(info->urb_ring_ref, 0,
+					  (unsigned long)info->urb_ring.sring);
+		info->urb_ring_ref = GRANT_INVALID_REF;
+	}
+	info->urb_ring.sring = NULL;
+
+	if (info->conn_ring_ref != GRANT_INVALID_REF) {
+		gnttab_end_foreign_access(info->conn_ring_ref, 0,
+					  (unsigned long)info->conn_ring.sring);
+		info->conn_ring_ref = GRANT_INVALID_REF;
+	}
+	info->conn_ring.sring = NULL;
+}
+
+static int xenhcd_setup_rings(struct xenbus_device *dev,
+			      struct xenhcd_info *info)
+{
+	struct xenusb_urb_sring *urb_sring;
+	struct xenusb_conn_sring *conn_sring;
+	grant_ref_t gref;
+	int err;
+
+	info->urb_ring_ref = GRANT_INVALID_REF;
+	info->conn_ring_ref = GRANT_INVALID_REF;
+
+	urb_sring = (struct xenusb_urb_sring *)get_zeroed_page(
+							GFP_NOIO | __GFP_HIGH);
+	if (!urb_sring) {
+		xenbus_dev_fatal(dev, -ENOMEM, "allocating urb ring");
+		return -ENOMEM;
+	}
+	SHARED_RING_INIT(urb_sring);
+	FRONT_RING_INIT(&info->urb_ring, urb_sring, PAGE_SIZE);
+
+	err = xenbus_grant_ring(dev, urb_sring, 1, &gref);
+	if (err < 0) {
+		free_page((unsigned long)urb_sring);
+		info->urb_ring.sring = NULL;
+		goto fail;
+	}
+	info->urb_ring_ref = gref;
+
+	conn_sring = (struct xenusb_conn_sring *)get_zeroed_page(
+							GFP_NOIO | __GFP_HIGH);
+	if (!conn_sring) {
+		xenbus_dev_fatal(dev, -ENOMEM, "allocating conn ring");
+		err = -ENOMEM;
+		goto fail;
+	}
+	SHARED_RING_INIT(conn_sring);
+	FRONT_RING_INIT(&info->conn_ring, conn_sring, PAGE_SIZE);
+
+	err = xenbus_grant_ring(dev, conn_sring, 1, &gref);
+	if (err < 0) {
+		free_page((unsigned long)conn_sring);
+		info->conn_ring.sring = NULL;
+		goto fail;
+	}
+	info->conn_ring_ref = gref;
+
+	err = xenbus_alloc_evtchn(dev, &info->evtchn);
+	if (err) {
+		xenbus_dev_fatal(dev, err, "xenbus_alloc_evtchn");
+		goto fail;
+	}
+
+	err = bind_evtchn_to_irq(info->evtchn);
+	if (err <= 0) {
+		xenbus_dev_fatal(dev, err, "bind_evtchn_to_irq");
+		goto fail;
+	}
+
+	info->irq = err;
+
+	err = request_threaded_irq(info->irq, NULL, xenhcd_int,
+				   IRQF_ONESHOT, "xenhcd", info);
+	if (err) {
+		xenbus_dev_fatal(dev, err, "request_threaded_irq");
+		goto free_irq;
+	}
+
+	return 0;
+
+free_irq:
+	unbind_from_irqhandler(info->irq, info);
+fail:
+	xenhcd_destroy_rings(info);
+	return err;
+}
+
+static int xenhcd_talk_to_backend(struct xenbus_device *dev,
+				  struct xenhcd_info *info)
+{
+	const char *message;
+	struct xenbus_transaction xbt;
+	int err;
+
+	err = xenhcd_setup_rings(dev, info);
+	if (err)
+		return err;
+
+again:
+	err = xenbus_transaction_start(&xbt);
+	if (err) {
+		xenbus_dev_fatal(dev, err, "starting transaction");
+		goto destroy_ring;
+	}
+
+	err = xenbus_printf(xbt, dev->nodename, "urb-ring-ref", "%u",
+			    info->urb_ring_ref);
+	if (err) {
+		message = "writing urb-ring-ref";
+		goto abort_transaction;
+	}
+
+	err = xenbus_printf(xbt, dev->nodename, "conn-ring-ref", "%u",
+			    info->conn_ring_ref);
+	if (err) {
+		message = "writing conn-ring-ref";
+		goto abort_transaction;
+	}
+
+	err = xenbus_printf(xbt, dev->nodename, "event-channel", "%u",
+			    info->evtchn);
+	if (err) {
+		message = "writing event-channel";
+		goto abort_transaction;
+	}
+
+	err = xenbus_transaction_end(xbt, 0);
+	if (err) {
+		if (err == -EAGAIN)
+			goto again;
+		xenbus_dev_fatal(dev, err, "completing transaction");
+		goto destroy_ring;
+	}
+
+	return 0;
+
+abort_transaction:
+	xenbus_transaction_end(xbt, 1);
+	xenbus_dev_fatal(dev, err, "%s", message);
+
+destroy_ring:
+	xenhcd_destroy_rings(info);
+
+	return err;
+}
+
+static int xenhcd_connect(struct xenbus_device *dev)
+{
+	struct xenhcd_info *info = dev_get_drvdata(&dev->dev);
+	struct xenusb_conn_request *req;
+	int idx, err;
+	int notify;
+	char name[TASK_COMM_LEN];
+	struct usb_hcd *hcd;
+
+	hcd = xenhcd_info_to_hcd(info);
+	snprintf(name, TASK_COMM_LEN, "xenhcd.%d", hcd->self.busnum);
+
+	err = xenhcd_talk_to_backend(dev, info);
+	if (err)
+		return err;
+
+	/* prepare ring for hotplug notification */
+	for (idx = 0; idx < XENUSB_CONN_RING_SIZE; idx++) {
+		req = RING_GET_REQUEST(&info->conn_ring, idx);
+		req->id = idx;
+	}
+	info->conn_ring.req_prod_pvt = idx;
+
+	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&info->conn_ring, notify);
+	if (notify)
+		notify_remote_via_irq(info->irq);
+
+	return 0;
+}
+
+static void xenhcd_disconnect(struct xenbus_device *dev)
+{
+	struct xenhcd_info *info = dev_get_drvdata(&dev->dev);
+	struct usb_hcd *hcd = xenhcd_info_to_hcd(info);
+
+	usb_remove_hcd(hcd);
+	xenbus_frontend_closed(dev);
+}
+
+static void xenhcd_watchdog(struct timer_list *timer)
+{
+	struct xenhcd_info *info = from_timer(info, timer, watchdog);
+	unsigned long flags;
+
+	spin_lock_irqsave(&info->lock, flags);
+	if (likely(HC_IS_RUNNING(xenhcd_info_to_hcd(info)->state))) {
+		xenhcd_timer_action_done(info, TIMER_RING_WATCHDOG);
+		xenhcd_giveback_unlinked_urbs(info);
+		xenhcd_kick_pending_urbs(info);
+	}
+	spin_unlock_irqrestore(&info->lock, flags);
+}
+
+/*
+ * one-time HC init
+ */
+static int xenhcd_setup(struct usb_hcd *hcd)
+{
+	struct xenhcd_info *info = xenhcd_hcd_to_info(hcd);
+
+	spin_lock_init(&info->lock);
+	INIT_LIST_HEAD(&info->pending_submit_list);
+	INIT_LIST_HEAD(&info->pending_unlink_list);
+	INIT_LIST_HEAD(&info->in_progress_list);
+	INIT_LIST_HEAD(&info->giveback_waiting_list);
+	timer_setup(&info->watchdog, xenhcd_watchdog, 0);
+
+	hcd->has_tt = (hcd->driver->flags & HCD_MASK) != HCD_USB11;
+
+	return 0;
+}
+
+/*
+ * start HC running
+ */
+static int xenhcd_run(struct usb_hcd *hcd)
+{
+	hcd->uses_new_polling = 1;
+	clear_bit(HCD_FLAG_POLL_RH, &hcd->flags);
+	hcd->state = HC_STATE_RUNNING;
+	return 0;
+}
+
+/*
+ * stop running HC
+ */
+static void xenhcd_stop(struct usb_hcd *hcd)
+{
+	struct xenhcd_info *info = xenhcd_hcd_to_info(hcd);
+
+	del_timer_sync(&info->watchdog);
+	spin_lock_irq(&info->lock);
+	/* cancel all urbs */
+	hcd->state = HC_STATE_HALT;
+	xenhcd_cancel_all_enqueued_urbs(info);
+	xenhcd_giveback_unlinked_urbs(info);
+	spin_unlock_irq(&info->lock);
+}
+
+/*
+ * called as .urb_enqueue()
+ * non-error returns are promise to giveback the urb later
+ */
+static int xenhcd_urb_enqueue(struct usb_hcd *hcd, struct urb *urb,
+			      gfp_t mem_flags)
+{
+	struct xenhcd_info *info = xenhcd_hcd_to_info(hcd);
+	struct urb_priv *urbp;
+	unsigned long flags;
+	int ret;
+
+	if (unlikely(info->error))
+		return -ESHUTDOWN;
+
+	urbp = kmem_cache_zalloc(xenhcd_urbp_cachep, mem_flags);
+	if (!urbp)
+		return -ENOMEM;
+
+	spin_lock_irqsave(&info->lock, flags);
+
+	urbp->urb = urb;
+	urb->hcpriv = urbp;
+	urbp->req_id = ~0;
+	urbp->unlink_req_id = ~0;
+	INIT_LIST_HEAD(&urbp->list);
+	urbp->status = 1;
+	urb->unlinked = false;
+
+	ret = xenhcd_submit_urb(info, urbp);
+
+	if (ret)
+		xenhcd_free_urb_priv(urbp);
+
+	spin_unlock_irqrestore(&info->lock, flags);
+
+	return ret;
+}
+
+/*
+ * called as .urb_dequeue()
+ */
+static int xenhcd_urb_dequeue(struct usb_hcd *hcd, struct urb *urb, int status)
+{
+	struct xenhcd_info *info = xenhcd_hcd_to_info(hcd);
+	struct urb_priv *urbp;
+	unsigned long flags;
+	int ret = 0;
+
+	spin_lock_irqsave(&info->lock, flags);
+
+	urbp = urb->hcpriv;
+	if (urbp) {
+		urbp->status = status;
+		ret = xenhcd_unlink_urb(info, urbp);
+	}
+
+	spin_unlock_irqrestore(&info->lock, flags);
+
+	return ret;
+}
+
+/*
+ * called from usb_get_current_frame_number(),
+ * but, almost all drivers not use such function.
+ */
+static int xenhcd_get_frame(struct usb_hcd *hcd)
+{
+	/* it means error, but probably no problem :-) */
+	return 0;
+}
+
+static struct hc_driver xenhcd_usb20_hc_driver = {
+	.description = "xen-hcd",
+	.product_desc = "Xen USB2.0 Virtual Host Controller",
+	.hcd_priv_size = sizeof(struct xenhcd_info),
+	.flags = HCD_USB2,
+
+	/* basic HC lifecycle operations */
+	.reset = xenhcd_setup,
+	.start = xenhcd_run,
+	.stop = xenhcd_stop,
+
+	/* managing urb I/O */
+	.urb_enqueue = xenhcd_urb_enqueue,
+	.urb_dequeue = xenhcd_urb_dequeue,
+	.get_frame_number = xenhcd_get_frame,
+
+	/* root hub operations */
+	.hub_status_data = xenhcd_hub_status_data,
+	.hub_control = xenhcd_hub_control,
+#ifdef CONFIG_PM
+	.bus_suspend = xenhcd_bus_suspend,
+	.bus_resume = xenhcd_bus_resume,
+#endif
+};
+
+static struct hc_driver xenhcd_usb11_hc_driver = {
+	.description = "xen-hcd",
+	.product_desc = "Xen USB1.1 Virtual Host Controller",
+	.hcd_priv_size = sizeof(struct xenhcd_info),
+	.flags = HCD_USB11,
+
+	/* basic HC lifecycle operations */
+	.reset = xenhcd_setup,
+	.start = xenhcd_run,
+	.stop = xenhcd_stop,
+
+	/* managing urb I/O */
+	.urb_enqueue = xenhcd_urb_enqueue,
+	.urb_dequeue = xenhcd_urb_dequeue,
+	.get_frame_number = xenhcd_get_frame,
+
+	/* root hub operations */
+	.hub_status_data = xenhcd_hub_status_data,
+	.hub_control = xenhcd_hub_control,
+#ifdef CONFIG_PM
+	.bus_suspend = xenhcd_bus_suspend,
+	.bus_resume = xenhcd_bus_resume,
+#endif
+};
+
+static struct usb_hcd *xenhcd_create_hcd(struct xenbus_device *dev)
+{
+	int i;
+	int err = 0;
+	int num_ports;
+	int usb_ver;
+	struct usb_hcd *hcd = NULL;
+	struct xenhcd_info *info;
+
+	err = xenbus_scanf(XBT_NIL, dev->otherend, "num-ports", "%d",
+			   &num_ports);
+	if (err != 1) {
+		xenbus_dev_fatal(dev, err, "reading num-ports");
+		return ERR_PTR(-EINVAL);
+	}
+	if (num_ports < 1 || num_ports > XENUSB_MAX_PORTNR) {
+		xenbus_dev_fatal(dev, err, "invalid num-ports");
+		return ERR_PTR(-EINVAL);
+	}
+
+	err = xenbus_scanf(XBT_NIL, dev->otherend, "usb-ver", "%d", &usb_ver);
+	if (err != 1) {
+		xenbus_dev_fatal(dev, err, "reading usb-ver");
+		return ERR_PTR(-EINVAL);
+	}
+	switch (usb_ver) {
+	case XENUSB_VER_USB11:
+		hcd = usb_create_hcd(&xenhcd_usb11_hc_driver, &dev->dev,
+				     dev_name(&dev->dev));
+		break;
+	case XENUSB_VER_USB20:
+		hcd = usb_create_hcd(&xenhcd_usb20_hc_driver, &dev->dev,
+				     dev_name(&dev->dev));
+		break;
+	default:
+		xenbus_dev_fatal(dev, err, "invalid usb-ver");
+		return ERR_PTR(-EINVAL);
+	}
+	if (!hcd) {
+		xenbus_dev_fatal(dev, err,
+				 "fail to allocate USB host controller");
+		return ERR_PTR(-ENOMEM);
+	}
+
+	info = xenhcd_hcd_to_info(hcd);
+	info->xbdev = dev;
+	info->rh_numports = num_ports;
+
+	for (i = 0; i < XENUSB_URB_RING_SIZE; i++) {
+		info->shadow[i].req.id = i + 1;
+		info->shadow[i].urb = NULL;
+	}
+	info->shadow[XENUSB_URB_RING_SIZE - 1].req.id = 0x0fff;
+
+	return hcd;
+}
+
+static void xenhcd_backend_changed(struct xenbus_device *dev,
+				   enum xenbus_state backend_state)
+{
+	switch (backend_state) {
+	case XenbusStateInitialising:
+	case XenbusStateReconfiguring:
+	case XenbusStateReconfigured:
+	case XenbusStateUnknown:
+		break;
+
+	case XenbusStateInitWait:
+	case XenbusStateInitialised:
+	case XenbusStateConnected:
+		if (dev->state != XenbusStateInitialising)
+			break;
+		if (!xenhcd_connect(dev))
+			xenbus_switch_state(dev, XenbusStateConnected);
+		break;
+
+	case XenbusStateClosed:
+		if (dev->state == XenbusStateClosed)
+			break;
+		fallthrough;	/* Missed the backend's Closing state. */
+	case XenbusStateClosing:
+		xenhcd_disconnect(dev);
+		break;
+
+	default:
+		xenbus_dev_fatal(dev, -EINVAL, "saw state %d at frontend",
+				 backend_state);
+		break;
+	}
+}
+
+static int xenhcd_remove(struct xenbus_device *dev)
+{
+	struct xenhcd_info *info = dev_get_drvdata(&dev->dev);
+	struct usb_hcd *hcd = xenhcd_info_to_hcd(info);
+
+	xenhcd_destroy_rings(info);
+	usb_put_hcd(hcd);
+
+	return 0;
+}
+
+static int xenhcd_probe(struct xenbus_device *dev,
+			const struct xenbus_device_id *id)
+{
+	int err;
+	struct usb_hcd *hcd;
+	struct xenhcd_info *info;
+
+	if (usb_disabled())
+		return -ENODEV;
+
+	hcd = xenhcd_create_hcd(dev);
+	if (IS_ERR(hcd)) {
+		err = PTR_ERR(hcd);
+		xenbus_dev_fatal(dev, err,
+				 "fail to create usb host controller");
+		return err;
+	}
+
+	info = xenhcd_hcd_to_info(hcd);
+	dev_set_drvdata(&dev->dev, info);
+
+	err = usb_add_hcd(hcd, 0, 0);
+	if (err) {
+		xenbus_dev_fatal(dev, err, "fail to add USB host controller");
+		usb_put_hcd(hcd);
+		dev_set_drvdata(&dev->dev, NULL);
+	}
+
+	return err;
+}
+
+static const struct xenbus_device_id xenhcd_ids[] = {
+	{ "vusb" },
+	{ "" },
+};
+
+static struct xenbus_driver xenhcd_driver = {
+	.ids			= xenhcd_ids,
+	.probe			= xenhcd_probe,
+	.otherend_changed	= xenhcd_backend_changed,
+	.remove			= xenhcd_remove,
+};
+
+static int __init xenhcd_init(void)
+{
+	if (!xen_domain())
+		return -ENODEV;
+
+	xenhcd_urbp_cachep = kmem_cache_create("xenhcd_urb_priv",
+					sizeof(struct urb_priv), 0, 0, NULL);
+	if (!xenhcd_urbp_cachep) {
+		pr_err("xenhcd failed to create kmem cache\n");
+		return -ENOMEM;
+	}
+
+	return xenbus_register_frontend(&xenhcd_driver);
+}
+module_init(xenhcd_init);
+
+static void __exit xenhcd_exit(void)
+{
+	kmem_cache_destroy(xenhcd_urbp_cachep);
+	xenbus_unregister_driver(&xenhcd_driver);
+}
+module_exit(xenhcd_exit);
+
+MODULE_ALIAS("xen:vusb");
+MODULE_AUTHOR("Juergen Gross <jgross@suse.com>");
+MODULE_DESCRIPTION("Xen USB Virtual Host Controller driver (xen-hcd)");
+MODULE_LICENSE("Dual BSD/GPL");