xen/kbdif: update protocol description

The patch clarifies the protocol that is used by the PV keyboard
drivers.
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Acked-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

include/xen/interface/io/kbdif.h

@@ -26,43 +26,223 @@
 #ifndef __XEN_PUBLIC_IO_KBDIF_H__
 #define __XEN_PUBLIC_IO_KBDIF_H__
 
-/* In events (backend -> frontend) */
+/*
+ *****************************************************************************
+ *                     Feature and Parameter Negotiation
+ *****************************************************************************
+ *
+ * The two halves of a para-virtual 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 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.
+ *
+ *****************************************************************************
+ *                            Backend XenBus Nodes
+ *****************************************************************************
+ *
+ *---------------------------- Features supported ----------------------------
+ *
+ * Capable backend advertises supported features by publishing
+ * corresponding entries in XenStore and puts 1 as the value of the entry.
+ * If a feature is not supported then 0 must be set or feature entry omitted.
+ *
+ * feature-abs-pointer
+ *      Values:         <uint>
+ *
+ *      Backends, which support reporting of absolute coordinates for pointer
+ *      device should set this to 1.
+ *
+ *------------------------- Pointer Device Parameters ------------------------
+ *
+ * width
+ *      Values:         <uint>
+ *
+ *      Maximum X coordinate (width) to be used by the frontend
+ *      while reporting input events, pixels, [0; UINT32_MAX].
+ *
+ * height
+ *      Values:         <uint>
+ *
+ *      Maximum Y coordinate (height) to be used by the frontend
+ *      while reporting input events, pixels, [0; UINT32_MAX].
+ *
+ *****************************************************************************
+ *                            Frontend XenBus Nodes
+ *****************************************************************************
+ *
+ *------------------------------ Feature request -----------------------------
+ *
+ * Capable frontend requests features from backend via setting corresponding
+ * entries to 1 in XenStore. Requests for features not advertised as supported
+ * by the backend have no effect.
+ *
+ * request-abs-pointer
+ *      Values:         <uint>
+ *
+ *      Request backend to report absolute pointer coordinates
+ *      (XENKBD_TYPE_POS) instead of relative ones (XENKBD_TYPE_MOTION).
+ *
+ *----------------------- Request Transport Parameters -----------------------
+ *
+ * event-channel
+ *      Values:         <uint>
+ *
+ *      The identifier of the Xen event channel used to signal activity
+ *      in the ring buffer.
+ *
+ * page-gref
+ *      Values:         <uint>
+ *
+ *      The Xen grant reference granting permission for the backend to map
+ *      a sole page in a single page sized event ring buffer.
+ *
+ * page-ref
+ *      Values:         <uint>
+ *
+ *      OBSOLETE, not recommended for use.
+ *      PFN of the shared page.
+ */
 
 /*
- * Frontends should ignore unknown in events.
+ * EVENT CODES.
  */
 
-/* Pointer movement event */
 #define XENKBD_TYPE_MOTION		1
-/* Event type 2 currently not used */
-/* Key event (includes pointer buttons) */
+#define XENKBD_TYPE_RESERVED		2
 #define XENKBD_TYPE_KEY			3
+#define XENKBD_TYPE_POS			4
+
 /*
- * Pointer position event
- * Capable backend sets feature-abs-pointer in xenstore.
- * Frontend requests ot instead of XENKBD_TYPE_MOTION by setting
- * request-abs-update in xenstore.
+ * CONSTANTS, XENSTORE FIELD AND PATH NAME STRINGS, HELPERS.
+ */
+
+#define XENKBD_DRIVER_NAME		"vkbd"
+
+#define XENKBD_FIELD_FEAT_ABS_POINTER	"feature-abs-pointer"
+#define XENKBD_FIELD_REQ_ABS_POINTER	"request-abs-pointer"
+#define XENKBD_FIELD_RING_GREF		"page-gref"
+#define XENKBD_FIELD_EVT_CHANNEL	"event-channel"
+#define XENKBD_FIELD_WIDTH		"width"
+#define XENKBD_FIELD_HEIGHT		"height"
+
+/* OBSOLETE, not recommended for use */
+#define XENKBD_FIELD_RING_REF		"page-ref"
+
+/*
+ *****************************************************************************
+ * Description of the protocol between frontend and backend driver.
+ *****************************************************************************
+ *
+ * The two halves of a Para-virtual driver communicate with
+ * each other using a shared page and an event channel.
+ * Shared page contains a ring with event structures.
+ *
+ * All reserved fields in the structures below must be 0.
+ *
+ *****************************************************************************
+ *                           Backend to frontend events
+ *****************************************************************************
+ *
+ * Frontends should ignore unknown in events.
+ * All event packets have the same length (40 octets)
+ * All event packets have common header:
+ *
+ *          0         octet
+ * +-----------------+
+ * |       type      |
+ * +-----------------+
+ * type - uint8_t, event code, XENKBD_TYPE_???
+ *
+ *
+ * Pointer relative movement event
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |  _TYPE_MOTION  |                     reserved                     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               rel_x                               | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                               rel_y                               | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                               rel_z                               | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 40
+ * +----------------+----------------+----------------+----------------+
+ *
+ * rel_x - int32_t, relative X motion
+ * rel_y - int32_t, relative Y motion
+ * rel_z - int32_t, relative Z motion (wheel)
  */
-#define XENKBD_TYPE_POS     4
 
 struct xenkbd_motion {
-	uint8_t type;		/* XENKBD_TYPE_MOTION */
-	int32_t rel_x;		/* relative X motion */
-	int32_t rel_y;		/* relative Y motion */
-	int32_t rel_z;		/* relative Z motion (wheel) */
+	uint8_t type;
+	int32_t rel_x;
+	int32_t rel_y;
+	int32_t rel_z;
 };
 
+/*
+ * Key event (includes pointer buttons)
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |  _TYPE_KEY     |     pressed    |            reserved             | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                              keycode                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 40
+ * +----------------+----------------+----------------+----------------+
+ *
+ * pressed - uint8_t, 1 if pressed; 0 otherwise
+ * keycode - uint32_t, KEY_* from linux/input.h
+ */
+
 struct xenkbd_key {
-	uint8_t type;		/* XENKBD_TYPE_KEY */
-	uint8_t pressed;	/* 1 if pressed; 0 otherwise */
-	uint32_t keycode;	/* KEY_* from linux/input.h */
+	uint8_t type;
+	uint8_t pressed;
+	uint32_t keycode;
 };
 
+/*
+ * Pointer absolute position event
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |  _TYPE_POS     |                     reserved                     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               abs_x                               | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                               abs_y                               | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                               rel_z                               | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 40
+ * +----------------+----------------+----------------+----------------+
+ *
+ * abs_x - int32_t, absolute X position (in FB pixels)
+ * abs_y - int32_t, absolute Y position (in FB pixels)
+ * rel_z - int32_t, relative Z motion (wheel)
+ */
+
 struct xenkbd_position {
-	uint8_t type;		/* XENKBD_TYPE_POS */
-	int32_t abs_x;		/* absolute X position (in FB pixels) */
-	int32_t abs_y;		/* absolute Y position (in FB pixels) */
-	int32_t rel_z;		/* relative Z motion (wheel) */
+	uint8_t type;
+	int32_t abs_x;
+	int32_t abs_y;
+	int32_t rel_z;
 };
 
 #define XENKBD_IN_EVENT_SIZE 40
@@ -75,12 +255,22 @@ union xenkbd_in_event {
 	char pad[XENKBD_IN_EVENT_SIZE];
 };
 
-/* Out events (frontend -> backend) */
-
 /*
+ *****************************************************************************
+ *                            Frontend to backend events
+ *****************************************************************************
+ *
  * Out events may be sent only when requested by backend, and receipt
  * of an unknown out event is an error.
  * No out events currently defined.
+
+ * All event packets have the same length (40 octets)
+ * All event packets have common header:
+ *          0         octet
+ * +-----------------+
+ * |       type      |
+ * +-----------------+
+ * type - uint8_t, event code
  */
 
 #define XENKBD_OUT_EVENT_SIZE 40
@@ -90,7 +280,11 @@ union xenkbd_out_event {
 	char pad[XENKBD_OUT_EVENT_SIZE];
 };
 
-/* shared page */
+/*
+ *****************************************************************************
+ *                            Shared page
+ *****************************************************************************
+ */
 
 #define XENKBD_IN_RING_SIZE 2048
 #define XENKBD_IN_RING_LEN (XENKBD_IN_RING_SIZE / XENKBD_IN_EVENT_SIZE)
@@ -113,4 +307,4 @@ struct xenkbd_page {
 	uint32_t out_cons, out_prod;
 };
 
-#endif
+#endif /* __XEN_PUBLIC_IO_KBDIF_H__ */