From a9a34e2b6abf756a94f8fd599fd8060cfc0e7a00 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Fri, 1 Oct 2021 15:11:28 +0200 Subject: 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 Reviewed-by: Luca Fancellu --- xen/include/public/io/usbif.h | 164 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 164 insertions(+) (limited to 'xen/include/public') 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//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 { -- cgit v1.2.3