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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v2 2/3] include/public: add better interface description to usbif.h
The PV USB protocol is poorly described. Add a more detailed
description to the usbif.h header file.
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
xen/include/public/io/usbif.h | 164 ++++++++++++++++++++++++++++++++++
1 file changed, 164 insertions(+)
diff --git a/xen/include/public/io/usbif.h b/xen/include/public/io/usbif.h
index 96b9fb661d..dd378bcba5 100644
--- a/xen/include/public/io/usbif.h
+++ b/xen/include/public/io/usbif.h
@@ -32,6 +32,34 @@
#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
@@ -99,6 +127,142 @@
* 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 USBIF_SPEED_*, USBIF_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[USBIF_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, USBIF_STATUS_* (non-iso requests)
+ * actual_length - uint32_t, actual size of data transferred
+ * error_count - uint32_t, number of errors (iso requests)
*/
enum usb_spec_version {
--
2.26.2
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