Disable middle mouse button emulation when a real middle MB event is detected.

Devices may report middle mouse buttons even if they don't have one (PS/2
devices just don't know any better), so we can't be sure until we see the
event.

man/evdev.man

@@ -60,8 +60,8 @@ one of \*qPath\*q or \*qDevice\*q must be given.
 .BI "Option \*qEmulate3Buttons\*q \*q" boolean \*q
 Enable/disable the emulation of the third (middle) mouse button for mice
 which only have two physical buttons.  The third button is emulated by
-pressing both buttons simultaneously.  Default: on, unless the device reports
-the presence of a physical button 3.
+pressing both buttons simultaneously.  Default: on, until a middle mouse
+button event is registered.
 .TP 7
 .BI "Option \*qEmulate3Timeout\*q \*q" integer \*q
 Sets the timeout (in milliseconds) that the driver waits before deciding

src/evdev.c

@@ -226,6 +226,7 @@ EvdevReadInput(InputInfoPtr pInfo)
                     xf86PostButtonEvent(pInfo->dev, 0, 3, value, 0, 0);
                 break;
             case BTN_MIDDLE:
+                EvdevMBEmuEnable(pInfo, FALSE);
                 xf86PostButtonEvent(pInfo->dev, 0, 2, value, 0, 0);
                 break;
 
@@ -943,12 +944,6 @@ EvdevProbe(InputInfoPtr pInfo)
 	has_buttons = TRUE;
     }
 
-    if (TestBit(BTN_MIDDLE, key_bitmask)) {
-        xf86Msg(X_INFO, "%s: Found middle button. Disabling emulation.\n",
-                pInfo->name);
-        EvdevMBEmuEnable(pInfo, FALSE);
-    }
-
     for (i = 0; i < BTN_MISC; i++)
         if (TestBit(i, key_bitmask))
             break;