This change adds support for horizontal scroll to ps/2 mouse device
code. The code is implemented to match the logic of linux kernel
which is used as a reference.

Signed-off-by: Dmitry Petrov <dpetroff@gmail.com>
---
 hw/input/ps2.c | 57 +++++++++++++++++++++++++++++++++++++++++++-------
 qapi/ui.json   |  2 +-
 2 files changed, 50 insertions(+), 9 deletions(-)

diff --git a/hw/input/ps2.c b/hw/input/ps2.c
index 9376a8f4ce..6236711e1b 100644
--- a/hw/input/ps2.c
+++ b/hw/input/ps2.c
@@ -123,6 +123,7 @@ typedef struct {
     int mouse_dx; /* current values, needed for 'poll' mode */
     int mouse_dy;
     int mouse_dz;
+    int mouse_dw;
     uint8_t mouse_buttons;
 } PS2MouseState;
 
@@ -715,7 +716,7 @@ static int ps2_mouse_send_packet(PS2MouseState *s)
     /* IMPS/2 and IMEX send 4 bytes, PS2 sends 3 bytes */
     const int needed = s->mouse_type ? 4 : 3;
     unsigned int b;
-    int dx1, dy1, dz1;
+    int dx1, dy1, dz1, dw1;
 
     if (PS2_QUEUE_SIZE - s->common.queue.count < needed) {
         return 0;
@@ -724,6 +725,7 @@ static int ps2_mouse_send_packet(PS2MouseState *s)
     dx1 = s->mouse_dx;
     dy1 = s->mouse_dy;
     dz1 = s->mouse_dz;
+    dw1 = s->mouse_dw;
     /* XXX: increase range to 8 bits ? */
     if (dx1 > 127)
         dx1 = 127;
@@ -740,6 +742,9 @@ static int ps2_mouse_send_packet(PS2MouseState *s)
     /* extra byte for IMPS/2 or IMEX */
     switch(s->mouse_type) {
     default:
+        /* Just ignore the wheels if not supported */
+        s->mouse_dz = 0;
+        s->mouse_dw = 0;
         break;
     case 3:
         if (dz1 > 127)
@@ -747,13 +752,41 @@ static int ps2_mouse_send_packet(PS2MouseState *s)
         else if (dz1 < -127)
                 dz1 = -127;
         ps2_queue_noirq(&s->common, dz1 & 0xff);
+        s->mouse_dz -= dz1;
+        s->mouse_dw = 0;
         break;
     case 4:
-        if (dz1 > 7)
-            dz1 = 7;
-        else if (dz1 < -7)
-            dz1 = -7;
-        b = (dz1 & 0x0f) | ((s->mouse_buttons & 0x18) << 1);
+        /*
+         * This matches what the Linux kernel expects for exps/2 in
+         * drivers/input/mouse/psmouse-base.c. Note, if you happen to
+         * press/release the 4th or 5th buttons at the same moment as a
+         * horizontal wheel scroll, those button presses will get lost. I'm not
+         * sure what to do about that, since by this point we don't know
+         * whether those buttons actually changed state.
+         */
+        if (dw1 != 0) {
+            if (dw1 > 31) {
+                dw1 = 31;
+            } else if (dw1 < -31) {
+                dw1 = -31;
+            }
+
+            /*
+             * linux kernel expects first 6 bits to represent the value
+             * for horizontal scroll
+             */
+            b = (dw1 & 0x3f) | 0x40;
+            s->mouse_dw -= dw1;
+        } else {
+            if (dz1 > 7) {
+                dz1 = 7;
+            } else if (dz1 < -7) {
+                dz1 = -7;
+            }
+
+            b = (dz1 & 0x0f) | ((s->mouse_buttons & 0x18) << 1);
+            s->mouse_dz -= dz1;
+        }
         ps2_queue_noirq(&s->common, b);
         break;
     }
@@ -764,7 +797,6 @@ static int ps2_mouse_send_packet(PS2MouseState *s)
     /* update deltas */
     s->mouse_dx -= dx1;
     s->mouse_dy -= dy1;
-    s->mouse_dz -= dz1;
 
     return 1;
 }
@@ -806,6 +838,12 @@ static void ps2_mouse_event(DeviceState *dev, QemuConsole *src,
             } else if (btn->button == INPUT_BUTTON_WHEEL_DOWN) {
                 s->mouse_dz++;
             }
+
+            if (btn->button == INPUT_BUTTON_WHEEL_RIGHT) {
+                s->mouse_dw--;
+            } else if (btn->button == INPUT_BUTTON_WHEEL_LEFT) {
+                s->mouse_dw++;
+            }
         } else {
             s->mouse_buttons &= ~bmap[btn->button];
         }
@@ -833,8 +871,10 @@ static void ps2_mouse_sync(DeviceState *dev)
         /* if not remote, send event. Multiple events are sent if
            too big deltas */
         while (ps2_mouse_send_packet(s)) {
-            if (s->mouse_dx == 0 && s->mouse_dy == 0 && s->mouse_dz == 0)
+            if (s->mouse_dx == 0 && s->mouse_dy == 0
+                    && s->mouse_dz == 0 && s->mouse_dw == 0) {
                 break;
+            }
         }
     }
 }
@@ -1036,6 +1076,7 @@ static void ps2_mouse_reset(void *opaque)
     s->mouse_dx = 0;
     s->mouse_dy = 0;
     s->mouse_dz = 0;
+    s->mouse_dw = 0;
     s->mouse_buttons = 0;
 }
 
diff --git a/qapi/ui.json b/qapi/ui.json
index 2b4371da37..9354f4c467 100644
--- a/qapi/ui.json
+++ b/qapi/ui.json
@@ -905,7 +905,7 @@
 ##
 { 'enum'  : 'InputButton',
   'data'  : [ 'left', 'middle', 'right', 'wheel-up', 'wheel-down', 'side',
-  'extra' ] }
+  'extra', 'wheel-left', 'wheel-right' ] }
 
 ##
 # @InputAxis:
-- 
2.32.0