FreeBSD/Linux Kernel Cross Reference
sys/xen/interface/io/displif.h

     /******************************************************************************
      * displif.h
      *
      * Unified display device I/O interface for Xen guest OSes.
      *
      * Permission is hereby granted, free of charge, to any person obtaining a copy
      * of this software and associated documentation files (the "Software"), to
      * deal in the Software without restriction, including without limitation the
      * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
     * sell copies of the Software, and to permit persons to whom the Software is
     * furnished to do so, subject to the following conditions:
     *
     * The above copyright notice and this permission notice shall be included in
     * all copies or substantial portions of the Software.
     *
     * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
     * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
     * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
     * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
     * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
     * DEALINGS IN THE SOFTWARE.
     *
     * Copyright (C) 2016-2017 EPAM Systems Inc.
     *
     * Authors: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
     *          Oleksandr Grytsov <oleksandr_grytsov@epam.com>
     */
    
    #ifndef __XEN_PUBLIC_IO_DISPLIF_H__
    #define __XEN_PUBLIC_IO_DISPLIF_H__
    
    #include "ring.h"
    #include "../grant_table.h"
    
    /*
     ******************************************************************************
     *                           Protocol version
     ******************************************************************************
     */
    #define XENDISPL_PROTOCOL_VERSION     "1"
    
    /*
     ******************************************************************************
     *                  Main features provided by the protocol
     ******************************************************************************
     * This protocol aims to provide a unified protocol which fits more
     * sophisticated use-cases than a framebuffer device can handle. At the
     * moment basic functionality is supported with the intention to be extended:
     *  o multiple dynamically allocated/destroyed framebuffers
     *  o buffers of arbitrary sizes
     *  o buffer allocation at either back or front end
     *  o better configuration options including multiple display support
     *
     * Note: existing fbif can be used together with displif running at the
     * same time, e.g. on Linux one provides framebuffer and another DRM/KMS
     *
     * Note: display resolution (XenStore's "resolution" property) defines
     * visible area of the virtual display. At the same time resolution of
     * the display and frame buffers may differ: buffers can be smaller, equal
     * or bigger than the visible area. This is to enable use-cases, where backend
     * may do some post-processing of the display and frame buffers supplied,
     * e.g. those buffers can be just a part of the final composition.
     *
     ******************************************************************************
     *                        Direction of improvements
     ******************************************************************************
     * Future extensions to the existing protocol may include:
     *  o display/connector cloning
     *  o allocation of objects other than display buffers
     *  o plane/overlay support
     *  o scaling support
     *  o rotation support
     *
     ******************************************************************************
     *                  Feature and Parameter Negotiation
     ******************************************************************************
     *
     * Front->back notifications: when enqueuing a new request, sending a
     * notification can be made conditional on xendispl_req (i.e., the generic
     * hold-off mechanism provided by the ring macros). Backends must set
     * xendispl_req appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
     *
     * Back->front notifications: when enqueuing a new response, sending a
     * notification can be made conditional on xendispl_resp (i.e., the generic
     * hold-off mechanism provided by the ring macros). Frontends must set
     * xendispl_resp appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
     *
     * The two halves of a para-virtual display driver utilize nodes within
     * XenStore to communicate capabilities and to negotiate operating parameters.
     * This section enumerates these nodes which reside in the respective front and
     * backend portions of XenStore, following the XenBus convention.
     *
     * All data in XenStore is stored as strings. Nodes specifying numeric
     * values are encoded in decimal. Integer value ranges listed below are
     * expressed as fixed sized integer types capable of storing the conversion
     * of a properly formated node string, without loss of information.
     *
     ******************************************************************************
    *                        Example configuration
    ******************************************************************************
    *
    * Note: depending on the use-case backend can expose more display connectors
    * than the underlying HW physically has by employing SW graphics compositors
    *
    * This is an example of backend and frontend configuration:
    *
    *--------------------------------- Backend -----------------------------------
    *
    * /local/domain/0/backend/vdispl/1/0/frontend-id = "1"
    * /local/domain/0/backend/vdispl/1/0/frontend = "/local/domain/1/device/vdispl/0"
    * /local/domain/0/backend/vdispl/1/0/state = "4"
    * /local/domain/0/backend/vdispl/1/0/versions = "1,2"
    *
    *--------------------------------- Frontend ----------------------------------
    *
    * /local/domain/1/device/vdispl/0/backend-id = ""
    * /local/domain/1/device/vdispl/0/backend = "/local/domain/0/backend/vdispl/1/0"
    * /local/domain/1/device/vdispl/0/state = "4"
    * /local/domain/1/device/vdispl/0/version = "1"
    * /local/domain/1/device/vdispl/0/be-alloc = "1"
    *
    *-------------------------- Connector 0 configuration ------------------------
    *
    * /local/domain/1/device/vdispl/0/0/resolution = "1920x1080"
    * /local/domain/1/device/vdispl/0/0/req-ring-ref = "2832"
    * /local/domain/1/device/vdispl/0/0/req-event-channel = "15"
    * /local/domain/1/device/vdispl/0/0/evt-ring-ref = "387"
    * /local/domain/1/device/vdispl/0/0/evt-event-channel = "16"
    *
    *-------------------------- Connector 1 configuration ------------------------
    *
    * /local/domain/1/device/vdispl/0/1/resolution = "800x600"
    * /local/domain/1/device/vdispl/0/1/req-ring-ref = "2833"
    * /local/domain/1/device/vdispl/0/1/req-event-channel = "17"
    * /local/domain/1/device/vdispl/0/1/evt-ring-ref = "388"
    * /local/domain/1/device/vdispl/0/1/evt-event-channel = "18"
    *
    ******************************************************************************
    *                            Backend XenBus Nodes
    ******************************************************************************
    *
    *----------------------------- Protocol version ------------------------------
    *
    * versions
    *      Values:         <string>
    *
    *      List of XENDISPL_LIST_SEPARATOR separated protocol versions supported
    *      by the backend. For example "1,2,3".
    *
    ******************************************************************************
    *                            Frontend XenBus Nodes
    ******************************************************************************
    *
    *-------------------------------- Addressing ---------------------------------
    *
    * dom-id
    *      Values:         <uint16_t>
    *
    *      Domain identifier.
    *
    * dev-id
    *      Values:         <uint16_t>
    *
    *      Device identifier.
    *
    * conn-idx
    *      Values:         <uint8_t>
    *
    *      Zero based contigous index of the connector.
    *      /local/domain/<dom-id>/device/vdispl/<dev-id>/<conn-idx>/...
    *
    *----------------------------- Protocol version ------------------------------
    *
    * version
    *      Values:         <string>
    *
    *      Protocol version, chosen among the ones supported by the backend.
    *
    *------------------------- Backend buffer allocation -------------------------
    *
    * be-alloc
    *      Values:         "", "1"
    *
    *      If value is set to "1", then backend can be a buffer provider/allocator
    *      for this domain during XENDISPL_OP_DBUF_CREATE operation (see below
    *      for negotiation).
    *      If value is not "1" or omitted frontend must allocate buffers itself.
    *
    *----------------------------- Connector settings ----------------------------
    *
    * unique-id
    *      Values:         <string>
    *
    *      After device instance initialization each connector is assigned a
    *      unique ID, so it can be identified by the backend by this ID.
    *      This can be UUID or such.
    *
    * resolution
    *      Values:         <width, uint32_t>x<height, uint32_t>
    *
    *      Width and height of the connector in pixels separated by
    *      XENDISPL_RESOLUTION_SEPARATOR. This defines visible area of the
    *      display.
    *
    *------------------ Connector Request Transport Parameters -------------------
    *
    * This communication path is used to deliver requests from frontend to backend
    * and get the corresponding responses from backend to frontend,
    * set up per connector.
    *
    * req-event-channel
    *      Values:         <uint32_t>
    *
    *      The identifier of the Xen connector's control event channel
    *      used to signal activity in the ring buffer.
    *
    * req-ring-ref
    *      Values:         <uint32_t>
    *
    *      The Xen grant reference granting permission for the backend to map
    *      a sole page of connector's control ring buffer.
    *
    *------------------- Connector Event Transport Parameters --------------------
    *
    * This communication path is used to deliver asynchronous events from backend
    * to frontend, set up per connector.
    *
    * evt-event-channel
    *      Values:         <uint32_t>
    *
    *      The identifier of the Xen connector's event channel
    *      used to signal activity in the ring buffer.
    *
    * evt-ring-ref
    *      Values:         <uint32_t>
    *
    *      The Xen grant reference granting permission for the backend to map
    *      a sole page of connector's event ring buffer.
    */
   
   /*
    ******************************************************************************
    *                               STATE DIAGRAMS
    ******************************************************************************
    *
    * Tool stack creates front and back state nodes with initial state
    * XenbusStateInitialising.
    * Tool stack creates and sets up frontend display configuration
    * nodes per domain.
    *
    *-------------------------------- Normal flow --------------------------------
    *
    * Front                                Back
    * =================================    =====================================
    * XenbusStateInitialising              XenbusStateInitialising
    *                                       o Query backend device identification
    *                                         data.
    *                                       o Open and validate backend device.
    *                                                |
    *                                                |
    *                                                V
    *                                      XenbusStateInitWait
    *
    * o Query frontend configuration
    * o Allocate and initialize
    *   event channels per configured
    *   connector.
    * o Publish transport parameters
    *   that will be in effect during
    *   this connection.
    *              |
    *              |
    *              V
    * XenbusStateInitialised
    *
    *                                       o Query frontend transport parameters.
    *                                       o Connect to the event channels.
    *                                                |
    *                                                |
    *                                                V
    *                                      XenbusStateConnected
    *
    *  o Create and initialize OS
    *    virtual display connectors
    *    as per configuration.
    *              |
    *              |
    *              V
    * XenbusStateConnected
    *
    *                                      XenbusStateUnknown
    *                                      XenbusStateClosed
    *                                      XenbusStateClosing
    * o Remove virtual display device
    * o Remove event channels
    *              |
    *              |
    *              V
    * XenbusStateClosed
    *
    *------------------------------- Recovery flow -------------------------------
    *
    * In case of frontend unrecoverable errors backend handles that as
    * if frontend goes into the XenbusStateClosed state.
    *
    * In case of backend unrecoverable errors frontend tries removing
    * the virtualized device. If this is possible at the moment of error,
    * then frontend goes into the XenbusStateInitialising state and is ready for
    * new connection with backend. If the virtualized device is still in use and
    * cannot be removed, then frontend goes into the XenbusStateReconfiguring state
    * until either the virtualized device is removed or backend initiates a new
    * connection. On the virtualized device removal frontend goes into the
    * XenbusStateInitialising state.
    *
    * Note on XenbusStateReconfiguring state of the frontend: if backend has
    * unrecoverable errors then frontend cannot send requests to the backend
    * and thus cannot provide functionality of the virtualized device anymore.
    * After backend is back to normal the virtualized device may still hold some
    * state: configuration in use, allocated buffers, client application state etc.
    * In most cases, this will require frontend to implement complex recovery
    * reconnect logic. Instead, by going into XenbusStateReconfiguring state,
    * frontend will make sure no new clients of the virtualized device are
    * accepted, allow existing client(s) to exit gracefully by signaling error
    * state etc.
    * Once all the clients are gone frontend can reinitialize the virtualized
    * device and get into XenbusStateInitialising state again signaling the
    * backend that a new connection can be made.
    *
    * There are multiple conditions possible under which frontend will go from
    * XenbusStateReconfiguring into XenbusStateInitialising, some of them are OS
    * specific. For example:
    * 1. The underlying OS framework may provide callbacks to signal that the last
    *    client of the virtualized device has gone and the device can be removed
    * 2. Frontend can schedule a deferred work (timer/tasklet/workqueue)
    *    to periodically check if this is the right time to re-try removal of
    *    the virtualized device.
    * 3. By any other means.
    *
    ******************************************************************************
    *                             REQUEST CODES
    ******************************************************************************
    * Request codes [0; 15] are reserved and must not be used
    */
   
   #define XENDISPL_OP_DBUF_CREATE       0x10
   #define XENDISPL_OP_DBUF_DESTROY      0x11
   #define XENDISPL_OP_FB_ATTACH         0x12
   #define XENDISPL_OP_FB_DETACH         0x13
   #define XENDISPL_OP_SET_CONFIG        0x14
   #define XENDISPL_OP_PG_FLIP           0x15
   
   /*
    ******************************************************************************
    *                                 EVENT CODES
    ******************************************************************************
    */
   #define XENDISPL_EVT_PG_FLIP          0x00
   
   /*
    ******************************************************************************
    *               XENSTORE FIELD AND PATH NAME STRINGS, HELPERS
    ******************************************************************************
    */
   #define XENDISPL_DRIVER_NAME          "vdispl"
   
   #define XENDISPL_LIST_SEPARATOR       ","
   #define XENDISPL_RESOLUTION_SEPARATOR "x"
   
   #define XENDISPL_FIELD_BE_VERSIONS    "versions"
   #define XENDISPL_FIELD_FE_VERSION     "version"
   #define XENDISPL_FIELD_REQ_RING_REF   "req-ring-ref"
   #define XENDISPL_FIELD_REQ_CHANNEL    "req-event-channel"
   #define XENDISPL_FIELD_EVT_RING_REF   "evt-ring-ref"
   #define XENDISPL_FIELD_EVT_CHANNEL    "evt-event-channel"
   #define XENDISPL_FIELD_RESOLUTION     "resolution"
   #define XENDISPL_FIELD_BE_ALLOC       "be-alloc"
   #define XENDISPL_FIELD_UNIQUE_ID      "unique-id"
   
   /*
    ******************************************************************************
    *                          STATUS RETURN CODES
    ******************************************************************************
    *
    * Status return code is zero on success and -XEN_EXX on failure.
    *
    ******************************************************************************
    *                              Assumptions
    ******************************************************************************
    * o usage of grant reference 0 as invalid grant reference:
    *   grant reference 0 is valid, but never exposed to a PV driver,
    *   because of the fact it is already in use/reserved by the PV console.
    * o all references in this document to page sizes must be treated
    *   as pages of size XEN_PAGE_SIZE unless otherwise noted.
    *
    ******************************************************************************
    *       Description of the protocol between frontend and backend driver
    ******************************************************************************
    *
    * The two halves of a Para-virtual display driver communicate with
    * each other using shared pages and event channels.
    * Shared page contains a ring with request/response packets.
    *
    * All reserved fields in the structures below must be 0.
    * Display buffers's cookie of value 0 is treated as invalid.
    * Framebuffer's cookie of value 0 is treated as invalid.
    *
    * For all request/response/event packets that use cookies:
    *   dbuf_cookie - uint64_t, unique to guest domain value used by the backend
    *     to map remote display buffer to its local one
    *   fb_cookie - uint64_t, unique to guest domain value used by the backend
    *     to map remote framebuffer to its local one
    *
    *---------------------------------- Requests ---------------------------------
    *
    * All requests/responses, which are not connector specific, must be sent over
    * control ring of the connector which has the index value of 0:
    *   /local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref
    *
    * All request packets have the same length (64 octets)
    * All request packets have common header:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |    operation   |   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    *   id - uint16_t, private guest value, echoed in response
    *   operation - uint8_t, operation code, XENDISPL_OP_???
    *
    * Request dbuf creation - request creation of a display buffer.
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |_OP_DBUF_CREATE |   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                       dbuf_cookie low 32-bit                      | 12
    * +----------------+----------------+----------------+----------------+
    * |                       dbuf_cookie high 32-bit                     | 16
    * +----------------+----------------+----------------+----------------+
    * |                               width                               | 20
    * +----------------+----------------+----------------+----------------+
    * |                               height                              | 24
    * +----------------+----------------+----------------+----------------+
    * |                                bpp                                | 28
    * +----------------+----------------+----------------+----------------+
    * |                             buffer_sz                             | 32
    * +----------------+----------------+----------------+----------------+
    * |                               flags                               | 36
    * +----------------+----------------+----------------+----------------+
    * |                           gref_directory                          | 40
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 44
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * Must be sent over control ring of the connector which has the index
    * value of 0:
    *   /local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref
    * All unused bits in flags field must be set to 0.
    *
    * An attempt to create multiple display buffers with the same dbuf_cookie is
    * an error. dbuf_cookie can be re-used after destroying the corresponding
    * display buffer.
    *
    * Width and height of the display buffers can be smaller, equal or bigger
    * than the connector's resolution. Depth/pixel format of the individual
    * buffers can differ as well.
    *
    * width - uint32_t, width in pixels
    * height - uint32_t, height in pixels
    * bpp - uint32_t, bits per pixel
    * buffer_sz - uint32_t, buffer size to be allocated, octets
    * flags - uint32_t, flags of the operation
    *   o XENDISPL_DBUF_FLG_REQ_ALLOC - if set, then backend is requested
    *     to allocate the buffer with the parameters provided in this request.
    *     Page directory is handled as follows:
    *       Frontend on request:
    *         o allocates pages for the directory (gref_directory,
    *           gref_dir_next_page(s)
    *         o grants permissions for the pages of the directory to the backend
    *         o sets gref_dir_next_page fields
    *       Backend on response:
    *         o grants permissions for the pages of the buffer allocated to
    *           the frontend
    *         o fills in page directory with grant references
    *           (gref[] in struct xendispl_page_directory)
    * gref_directory - grant_ref_t, a reference to the first shared page
    *   describing shared buffer references. At least one page exists. If shared
    *   buffer size (buffer_sz) exceeds what can be addressed by this single page,
    *   then reference to the next page must be supplied (see gref_dir_next_page
    *   below)
    */
   
   #define XENDISPL_DBUF_FLG_REQ_ALLOC       (1 << 0)
   
   struct xendispl_dbuf_create_req {
       uint64_t dbuf_cookie;
       uint32_t width;
       uint32_t height;
       uint32_t bpp;
       uint32_t buffer_sz;
       uint32_t flags;
       grant_ref_t gref_directory;
   };
   
   /*
    * Shared page for XENDISPL_OP_DBUF_CREATE buffer descriptor (gref_directory in
    * the request) employs a list of pages, describing all pages of the shared
    * data buffer:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |                        gref_dir_next_page                         | 4
    * +----------------+----------------+----------------+----------------+
    * |                              gref[0]                              | 8
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                              gref[i]                              | i*4+8
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             gref[N - 1]                           | N*4+8
    * +----------------+----------------+----------------+----------------+
    *
    * gref_dir_next_page - grant_ref_t, reference to the next page describing
    *   page directory. Must be 0 if there are no more pages in the list.
    * gref[i] - grant_ref_t, reference to a shared page of the buffer
    *   allocated at XENDISPL_OP_DBUF_CREATE
    *
    * Number of grant_ref_t entries in the whole page directory is not
    * passed, but instead can be calculated as:
    *   num_grefs_total = (XENDISPL_OP_DBUF_CREATE.buffer_sz + XEN_PAGE_SIZE - 1) /
    *       XEN_PAGE_SIZE
    */
   
   struct xendispl_page_directory {
       grant_ref_t gref_dir_next_page;
       grant_ref_t gref[1]; /* Variable length */
   };
   
   /*
    * Request dbuf destruction - destroy a previously allocated display buffer:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |_OP_DBUF_DESTROY|   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                       dbuf_cookie low 32-bit                      | 12
    * +----------------+----------------+----------------+----------------+
    * |                       dbuf_cookie high 32-bit                     | 16
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 20
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * Must be sent over control ring of the connector which has the index
    * value of 0:
    *   /local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref
    */
   
   struct xendispl_dbuf_destroy_req {
       uint64_t dbuf_cookie;
   };
   
   /*
    * Request framebuffer attachment - request attachment of a framebuffer to
    * previously created display buffer.
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                | _OP_FB_ATTACH  |   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                       dbuf_cookie low 32-bit                      | 12
    * +----------------+----------------+----------------+----------------+
    * |                       dbuf_cookie high 32-bit                     | 16
    * +----------------+----------------+----------------+----------------+
    * |                        fb_cookie low 32-bit                       | 20
    * +----------------+----------------+----------------+----------------+
    * |                        fb_cookie high 32-bit                      | 24
    * +----------------+----------------+----------------+----------------+
    * |                               width                               | 28
    * +----------------+----------------+----------------+----------------+
    * |                               height                              | 32
    * +----------------+----------------+----------------+----------------+
    * |                            pixel_format                           | 36
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 40
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * Must be sent over control ring of the connector which has the index
    * value of 0:
    *   /local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref
    * Width and height can be smaller, equal or bigger than the connector's
    * resolution.
    *
    * An attempt to create multiple frame buffers with the same fb_cookie is
    * an error. fb_cookie can be re-used after destroying the corresponding
    * frame buffer.
    *
    * width - uint32_t, width in pixels
    * height - uint32_t, height in pixels
    * pixel_format - uint32_t, pixel format of the framebuffer, FOURCC code
    */
   
   struct xendispl_fb_attach_req {
       uint64_t dbuf_cookie;
       uint64_t fb_cookie;
       uint32_t width;
       uint32_t height;
       uint32_t pixel_format;
   };
   
   /*
    * Request framebuffer detach - detach a previously
    * attached framebuffer from the display buffer in request:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |  _OP_FB_DETACH |   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                        fb_cookie low 32-bit                       | 12
    * +----------------+----------------+----------------+----------------+
    * |                        fb_cookie high 32-bit                      | 16
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 20
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * Must be sent over control ring of the connector which has the index
    * value of 0:
    *   /local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref
    */
   
   struct xendispl_fb_detach_req {
       uint64_t fb_cookie;
   };
   
   /*
    * Request configuration set/reset - request to set or reset
    * the configuration/mode of the display:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                | _OP_SET_CONFIG |   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                        fb_cookie low 32-bit                       | 12
    * +----------------+----------------+----------------+----------------+
    * |                        fb_cookie high 32-bit                      | 16
    * +----------------+----------------+----------------+----------------+
    * |                                 x                                 | 20
    * +----------------+----------------+----------------+----------------+
    * |                                 y                                 | 24
    * +----------------+----------------+----------------+----------------+
    * |                               width                               | 28
    * +----------------+----------------+----------------+----------------+
    * |                               height                              | 32
    * +----------------+----------------+----------------+----------------+
    * |                                bpp                                | 40
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 44
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * Pass all zeros to reset, otherwise command is treated as
    * configuration set.
    * Framebuffer's cookie defines which framebuffer/dbuf must be
    * displayed while enabling display (applying configuration).
    * x, y, width and height are bound by the connector's resolution and must not
    * exceed it.
    *
    * x - uint32_t, starting position in pixels by X axis
    * y - uint32_t, starting position in pixels by Y axis
    * width - uint32_t, width in pixels
    * height - uint32_t, height in pixels
    * bpp - uint32_t, bits per pixel
    */
   
   struct xendispl_set_config_req {
       uint64_t fb_cookie;
       uint32_t x;
       uint32_t y;
       uint32_t width;
       uint32_t height;
       uint32_t bpp;
   };
   
   /*
    * Request page flip - request to flip a page identified by the framebuffer
    * cookie:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                | _OP_PG_FLIP    |   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                        fb_cookie low 32-bit                       | 12
    * +----------------+----------------+----------------+----------------+
    * |                        fb_cookie high 32-bit                      | 16
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 20
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    */
   
   struct xendispl_page_flip_req {
       uint64_t fb_cookie;
   };
   
   /*
    *---------------------------------- Responses --------------------------------
    *
    * All response packets have the same length (64 octets)
    *
    * All response packets have common header:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |            reserved             | 4
    * +----------------+----------------+----------------+----------------+
    * |                              status                               | 8
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 12
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    *
    * id - uint16_t, private guest value, echoed from request
    * status - int32_t, response status, zero on success and -XEN_EXX on failure
    *
    *----------------------------------- Events ----------------------------------
    *
    * Events are sent via a shared page allocated by the front and propagated by
    *   evt-event-channel/evt-ring-ref XenStore entries
    * All event packets have the same length (64 octets)
    * All event packets have common header:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |      type      |   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    *
    * id - uint16_t, event id, may be used by front
    * type - uint8_t, type of the event
    *
    *
    * Page flip complete event - event from back to front on page flip completed:
    *         0                1                 2               3        octet
    * +----------------+----------------+----------------+----------------+
    * |               id                |   _EVT_PG_FLIP |   reserved     | 4
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 8
    * +----------------+----------------+----------------+----------------+
    * |                        fb_cookie low 32-bit                       | 12
    * +----------------+----------------+----------------+----------------+
    * |                        fb_cookie high 32-bit                      | 16
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 20
    * +----------------+----------------+----------------+----------------+
    * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
    * +----------------+----------------+----------------+----------------+
    * |                             reserved                              | 64
    * +----------------+----------------+----------------+----------------+
    */
   
   struct xendispl_pg_flip_evt {
       uint64_t fb_cookie;
   };
   
   struct xendispl_req {
       uint16_t id;
       uint8_t operation;
       uint8_t reserved[5];
       union {
           struct xendispl_dbuf_create_req dbuf_create;
           struct xendispl_dbuf_destroy_req dbuf_destroy;
           struct xendispl_fb_attach_req fb_attach;
           struct xendispl_fb_detach_req fb_detach;
           struct xendispl_set_config_req set_config;
           struct xendispl_page_flip_req pg_flip;
           uint8_t reserved[56];
       } op;
   };
   
   struct xendispl_resp {
       uint16_t id;
       uint8_t operation;
       uint8_t reserved;
       int32_t status;
       uint8_t reserved1[56];
   };
   
   struct xendispl_evt {
       uint16_t id;
       uint8_t type;
       uint8_t reserved[5];
       union {
           struct xendispl_pg_flip_evt pg_flip;
           uint8_t reserved[56];
       } op;
   };
   
   DEFINE_RING_TYPES(xen_displif, struct xendispl_req, struct xendispl_resp);
   
   /*
    ******************************************************************************
    *                        Back to front events delivery
    ******************************************************************************
    * In order to deliver asynchronous events from back to front a shared page is
    * allocated by front and its granted reference propagated to back via
    * XenStore entries (evt-ring-ref/evt-event-channel).
    * This page has a common header used by both front and back to synchronize
    * access and control event's ring buffer, while back being a producer of the
    * events and front being a consumer. The rest of the page after the header
    * is used for event packets.
    *
    * Upon reception of an event(s) front may confirm its reception
    * for either each event, group of events or none.
    */
   
   struct xendispl_event_page {
       uint32_t in_cons;
       uint32_t in_prod;
       uint8_t reserved[56];
   };
   
   #define XENDISPL_EVENT_PAGE_SIZE 4096
   #define XENDISPL_IN_RING_OFFS (sizeof(struct xendispl_event_page))
   #define XENDISPL_IN_RING_SIZE (XENDISPL_EVENT_PAGE_SIZE - XENDISPL_IN_RING_OFFS)
   #define XENDISPL_IN_RING_LEN (XENDISPL_IN_RING_SIZE / sizeof(struct xendispl_evt))
   #define XENDISPL_IN_RING(page) \
           ((struct xendispl_evt *)((char *)(page) + XENDISPL_IN_RING_OFFS))
   #define XENDISPL_IN_RING_REF(page, idx) \
           (XENDISPL_IN_RING((page))[(idx) % XENDISPL_IN_RING_LEN])
   
   #endif /* __XEN_PUBLIC_IO_DISPLIF_H__ */
   
   /*
    * Local variables:
    * mode: C
    * c-file-style: "BSD"
    * c-basic-offset: 4
    * tab-width: 4
    * indent-tabs-mode: nil
    * End:
    */

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