usb: Add Xen pvUSB protocol description

Add the definition of pvUSB protocol used between the pvUSB frontend in
a Xen domU and the pvUSB backend in a Xen driver domain (usually Dom0).

This header was originally provided by Fujitsu for Xen based on Linux
2.6.18.

Changes are:
- adapt to Linux kernel style guide
- use Xen namespace
- add lots of comments
- don't use kernel internal defines

Reviewed-by: Boris Ostrovsky <[e-mail]>
Signed-off-by: Juergen Gross <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/xen/interface/io/usbif.h

···
+/* SPDX-License-Identifier: MIT */
+
+/*
+ * usbif.h
+ *
+ * USB I/O interface for Xen guest OSes.
+ *
+ * Copyright (C) 2009, FUJITSU LABORATORIES LTD.
+ * Author: Noboru Iwamatsu <[e-mail]>
+ */
+
+#ifndef __XEN_PUBLIC_IO_USBIF_H__
+#define __XEN_PUBLIC_IO_USBIF_H__
+
+#include "ring.h"
+#include "../grant_table.h"
+
+/*
+ * Detailed Interface Description
+ * ==============================
+ * The pvUSB interface is using a split driver design: a frontend driver in
+ * the guest and a backend driver in a driver domain (normally dom0) having
+ * access to the physical USB device(s) being passed to the guest.
+ *
+ * The frontend and backend drivers use XenStore to initiate the connection
+ * between them, the I/O activity is handled via two shared ring pages and an
+ * event channel. As the interface between frontend and backend is at the USB
+ * host connector level, multiple (up to 31) physical USB devices can be
+ * handled by a single connection.
+ *
+ * The Xen pvUSB device name is "qusb", so the frontend's XenStore entries are
+ * to be found under "device/qusb", while the backend's XenStore entries are
+ * under "backend/<guest-dom-id>/qusb".
+ *
+ * When a new pvUSB connection is established, the frontend needs to setup the
+ * two shared ring pages for communication and the event channel. The ring
+ * pages need to be made available to the backend via the grant table
+ * interface.
+ *
+ * One of the shared ring pages is used by the backend to inform the frontend
+ * about USB device plug events (device to be added or removed). This is the
+ * "conn-ring".
+ *
+ * The other ring page is used for USB I/O communication (requests and
+ * responses). This is the "urb-ring".
+ *
+ * Feature and Parameter Negotiation
+ * =================================
+ * The two halves of a Xen pvUSB driver utilize nodes within the XenStore to
+ * communicate capabilities and to negotiate operating parameters. This
+ * section enumerates these nodes which reside in the respective front and
+ * backend portions of the XenStore, following the XenBus convention.
+ *
+ * Any specified default value is in effect if the corresponding XenBus node
+ * is not present in the XenStore.
+ *
+ * XenStore nodes in sections marked "PRIVATE" are solely for use by the
+ * driver side whose XenBus tree contains them.
+ *
+ *****************************************************************************
+ *                            Backend XenBus Nodes
+ *****************************************************************************
+ *
+ *------------------ Backend Device Identification (PRIVATE) ------------------
+ *
+ * num-ports
+ *      Values:         unsigned [1...31]
+ *
+ *      Number of ports for this (virtual) USB host connector.
+ *
+ * usb-ver
+ *      Values:         unsigned [1...2]
+ *
+ *      USB version of this host connector: 1 = USB 1.1, 2 = USB 2.0.
+ *
+ * port/[1...31]
+ *      Values:         string
+ *
+ *      Physical USB device connected to the given port, e.g. "3-1.5".
+ *
+ *****************************************************************************
+ *                            Frontend XenBus Nodes
+ *****************************************************************************
+ *
+ *----------------------- Request Transport Parameters -----------------------
+ *
+ * event-channel
+ *      Values:         unsigned
+ *
+ *      The identifier of the Xen event channel used to signal activity
+ *      in the ring buffer.
+ *
+ * urb-ring-ref
+ *      Values:         unsigned
+ *
+ *      The Xen grant reference granting permission for the backend to map
+ *      the sole page in a single page sized ring buffer. This is the ring
+ *      buffer for urb requests.
+ *
+ * conn-ring-ref
+ *      Values:         unsigned
+ *
+ *      The Xen grant reference granting permission for the backend to map
+ *      the sole page in a single page sized ring buffer. This is the ring
+ *      buffer for connection/disconnection requests.
+ *
+ * protocol
+ *      Values:         string (XEN_IO_PROTO_ABI_*)
+ *      Default Value:  XEN_IO_PROTO_ABI_NATIVE
+ *
+ *      The machine ABI rules governing the format of all ring request and
+ *      response structures.
+ *
+ * Protocol Description
+ * ====================
+ *
+ *-------------------------- USB device plug events --------------------------
+ *
+ * USB device plug events are send via the "conn-ring" shared page. As only
+ * events are being sent, the respective requests from the frontend to the
+ * backend are just dummy ones.
+ * The events sent to the frontend have the following layout:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |    portnum     |     speed      | 4
+ * +----------------+----------------+----------------+----------------+
+ *   id - uint16_t, event id (taken from the actual frontend dummy request)
+ *   portnum - uint8_t, port number (1 ... 31)
+ *   speed - uint8_t, device XENUSB_SPEED_*, XENUSB_SPEED_NONE == unplug
+ *
+ * The dummy request:
+ *         0                1        octet
+ * +----------------+----------------+
+ * |               id                | 2
+ * +----------------+----------------+
+ *   id - uint16_t, guest supplied value (no need for being unique)
+ *
+ *-------------------------- USB I/O request ---------------------------------
+ *
+ * A single USB I/O request on the "urb-ring" has the following layout:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |         nr_buffer_segs          | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               pipe                                | 8
+ * +----------------+----------------+----------------+----------------+
+ * |         transfer_flags          |          buffer_length          | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                       request type specific                       | 16
+ * |                               data                                | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                              seg[0]                               | 24
+ * |                               data                                | 28
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |             seg[XENUSB_MAX_SEGMENTS_PER_REQUEST - 1]              | 144
+ * |                               data                                | 148
+ * +----------------+----------------+----------------+----------------+
+ * Bit field bit number 0 is always least significant bit, undefined bits must
+ * be zero.
+ *   id - uint16_t, guest supplied value
+ *   nr_buffer_segs - uint16_t, number of segment entries in seg[] array
+ *   pipe - uint32_t, bit field with multiple information:
+ *     bits 0-4: port request to send to
+ *     bit 5: unlink request with specified id (cancel I/O) if set (see below)
+ *     bit 7: direction (1 = read from device)
+ *     bits 8-14: device number on port
+ *     bits 15-18: endpoint of device
+ *     bits 30-31: request type: 00 = isochronous, 01 = interrupt,
+ *                               10 = control, 11 = bulk
+ *   transfer_flags - uint16_t, bit field with processing flags:
+ *     bit 0: less data than specified allowed
+ *   buffer_length - uint16_t, total length of data
+ *   request type specific data - 8 bytes, see below
+ *   seg[] - array with 8 byte elements, see below
+ *
+ * Request type specific data for isochronous request:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |            interval             |           start_frame           | 4
+ * +----------------+----------------+----------------+----------------+
+ * |       number_of_packets         |       nr_frame_desc_segs        | 8
+ * +----------------+----------------+----------------+----------------+
+ *   interval - uint16_t, time interval in msecs between frames
+ *   start_frame - uint16_t, start frame number
+ *   number_of_packets - uint16_t, number of packets to transfer
+ *   nr_frame_desc_segs - uint16_t number of seg[] frame descriptors elements
+ *
+ * Request type specific data for interrupt request:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |            interval             |                0                | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                                 0                                 | 8
+ * +----------------+----------------+----------------+----------------+
+ *   interval - uint16_t, time in msecs until interruption
+ *
+ * Request type specific data for control request:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |                      data of setup packet                         | 4
+ * |                                                                   | 8
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Request type specific data for bulk request:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |                                 0                                 | 4
+ * |                                 0                                 | 8
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Request type specific data for unlink request:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |           unlink_id             |                0                | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                                 0                                 | 8
+ * +----------------+----------------+----------------+----------------+
+ *   unlink_id - uint16_t, request id of request to terminate
+ *
+ * seg[] array element layout:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |                               gref                                | 4
+ * +----------------+----------------+----------------+----------------+
+ * |             offset              |             length              | 8
+ * +----------------+----------------+----------------+----------------+
+ *   gref - uint32_t, grant reference of buffer page
+ *   offset - uint16_t, offset of buffer start in page
+ *   length - uint16_t, length of buffer in page
+ *
+ *-------------------------- USB I/O response --------------------------------
+ *
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |          start_frame            | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                              status                               | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                          actual_length                            | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                           error_count                             | 16
+ * +----------------+----------------+----------------+----------------+
+ *   id - uint16_t, id of the request this response belongs to
+ *   start_frame - uint16_t, start_frame this response (iso requests only)
+ *   status - int32_t, XENUSB_STATUS_* (non-iso requests)
+ *   actual_length - uint32_t, actual size of data transferred
+ *   error_count - uint32_t, number of errors (iso requests)
+ */
+
+enum xenusb_spec_version {
+	XENUSB_VER_UNKNOWN = 0,
+	XENUSB_VER_USB11,
+	XENUSB_VER_USB20,
+	XENUSB_VER_USB30,	/* not supported yet */
+};
+
+/*
+ *  USB pipe in xenusb_request
+ *
+ *  - port number:      bits 0-4
+ *                              (USB_MAXCHILDREN is 31)
+ *
+ *  - operation flag:   bit 5
+ *                              (0 = submit urb,
+ *                               1 = unlink urb)
+ *
+ *  - direction:        bit 7
+ *                              (0 = Host-to-Device [Out]
+ *                               1 = Device-to-Host [In])
+ *
+ *  - device address:   bits 8-14
+ *
+ *  - endpoint:         bits 15-18
+ *
+ *  - pipe type:        bits 30-31
+ *                              (00 = isochronous, 01 = interrupt,
+ *                               10 = control, 11 = bulk)
+ */
+
+#define XENUSB_PIPE_PORT_MASK	0x0000001f
+#define XENUSB_PIPE_UNLINK	0x00000020
+#define XENUSB_PIPE_DIR		0x00000080
+#define XENUSB_PIPE_DEV_MASK	0x0000007f
+#define XENUSB_PIPE_DEV_SHIFT	8
+#define XENUSB_PIPE_EP_MASK	0x0000000f
+#define XENUSB_PIPE_EP_SHIFT	15
+#define XENUSB_PIPE_TYPE_MASK	0x00000003
+#define XENUSB_PIPE_TYPE_SHIFT	30
+#define XENUSB_PIPE_TYPE_ISOC	0
+#define XENUSB_PIPE_TYPE_INT	1
+#define XENUSB_PIPE_TYPE_CTRL	2
+#define XENUSB_PIPE_TYPE_BULK	3
+
+#define xenusb_pipeportnum(pipe)		((pipe) & XENUSB_PIPE_PORT_MASK)
+#define xenusb_setportnum_pipe(pipe, portnum)	((pipe) | (portnum))
+
+#define xenusb_pipeunlink(pipe)			((pipe) & XENUSB_PIPE_UNLINK)
+#define xenusb_pipesubmit(pipe)			(!xenusb_pipeunlink(pipe))
+#define xenusb_setunlink_pipe(pipe)		((pipe) | XENUSB_PIPE_UNLINK)
+
+#define xenusb_pipein(pipe)			((pipe) & XENUSB_PIPE_DIR)
+#define xenusb_pipeout(pipe)			(!xenusb_pipein(pipe))
+
+#define xenusb_pipedevice(pipe)			\
+	(((pipe) >> XENUSB_PIPE_DEV_SHIFT) & XENUSB_PIPE_DEV_MASK)
+
+#define xenusb_pipeendpoint(pipe)		\
+	(((pipe) >> XENUSB_PIPE_EP_SHIFT) & XENUSB_PIPE_EP_MASK)
+
+#define xenusb_pipetype(pipe)			\
+	(((pipe) >> XENUSB_PIPE_TYPE_SHIFT) & XENUSB_PIPE_TYPE_MASK)
+#define xenusb_pipeisoc(pipe)	(xenusb_pipetype(pipe) == XENUSB_PIPE_TYPE_ISOC)
+#define xenusb_pipeint(pipe)	(xenusb_pipetype(pipe) == XENUSB_PIPE_TYPE_INT)
+#define xenusb_pipectrl(pipe)	(xenusb_pipetype(pipe) == XENUSB_PIPE_TYPE_CTRL)
+#define xenusb_pipebulk(pipe)	(xenusb_pipetype(pipe) == XENUSB_PIPE_TYPE_BULK)
+
+#define XENUSB_MAX_SEGMENTS_PER_REQUEST (16)
+#define XENUSB_MAX_PORTNR		31
+#define XENUSB_RING_SIZE		4096
+
+/*
+ * RING for transferring urbs.
+ */
+struct xenusb_request_segment {
+	grant_ref_t gref;
+	uint16_t offset;
+	uint16_t length;
+};
+
+struct xenusb_urb_request {
+	uint16_t id;			/* request id */
+	uint16_t nr_buffer_segs;	/* number of urb->transfer_buffer segments */
+
+	/* basic urb parameter */
+	uint32_t pipe;
+	uint16_t transfer_flags;
+#define XENUSB_SHORT_NOT_OK	0x0001
+	uint16_t buffer_length;
+	union {
+		uint8_t ctrl[8];	/* setup_packet (Ctrl) */
+
+		struct {
+			uint16_t interval;	/* maximum (1024*8) in usb core */
+			uint16_t start_frame;	/* start frame */
+			uint16_t number_of_packets;	/* number of ISO packet */
+			uint16_t nr_frame_desc_segs;	/* number of iso_frame_desc segments */
+		} isoc;
+
+		struct {
+			uint16_t interval;	/* maximum (1024*8) in usb core */
+			uint16_t pad[3];
+		} intr;
+
+		struct {
+			uint16_t unlink_id;	/* unlink request id */
+			uint16_t pad[3];
+		} unlink;
+
+	} u;
+
+	/* urb data segments */
+	struct xenusb_request_segment seg[XENUSB_MAX_SEGMENTS_PER_REQUEST];
+};
+
+struct xenusb_urb_response {
+	uint16_t id;		/* request id */
+	uint16_t start_frame;	/* start frame (ISO) */
+	int32_t status;		/* status (non-ISO) */
+#define XENUSB_STATUS_OK	0
+#define XENUSB_STATUS_NODEV	(-19)
+#define XENUSB_STATUS_INVAL	(-22)
+#define XENUSB_STATUS_STALL	(-32)
+#define XENUSB_STATUS_IOERROR	(-71)
+#define XENUSB_STATUS_BABBLE	(-75)
+#define XENUSB_STATUS_SHUTDOWN	(-108)
+	int32_t actual_length;	/* actual transfer length */
+	int32_t error_count;	/* number of ISO errors */
+};
+
+DEFINE_RING_TYPES(xenusb_urb, struct xenusb_urb_request, struct xenusb_urb_response);
+#define XENUSB_URB_RING_SIZE __CONST_RING_SIZE(xenusb_urb, XENUSB_RING_SIZE)
+
+/*
+ * RING for notifying connect/disconnect events to frontend
+ */
+struct xenusb_conn_request {
+	uint16_t id;
+};
+
+struct xenusb_conn_response {
+	uint16_t id;		/* request id */
+	uint8_t portnum;	/* port number */
+	uint8_t speed;		/* usb_device_speed */
+#define XENUSB_SPEED_NONE	0
+#define XENUSB_SPEED_LOW	1
+#define XENUSB_SPEED_FULL	2
+#define XENUSB_SPEED_HIGH	3
+};
+
+DEFINE_RING_TYPES(xenusb_conn, struct xenusb_conn_request, struct xenusb_conn_response);
+#define XENUSB_CONN_RING_SIZE __CONST_RING_SIZE(xenusb_conn, XENUSB_RING_SIZE)
+
+#endif /* __XEN_PUBLIC_IO_USBIF_H__ */