ACPI video: allow events handlers to veto the keypress

The standard video events may be overloaded for device specific
purposes. For example AMD ACPI interface overloads
ACPI_VIDEO_NOTIFY_PROBE (0x81) to signal AMD-specific events. In such
cases we don't want to send the keypress (KEY_SWITCHVIDEOMODE) to the
userspace because the user did not press the mode switch key (the
spurious keypress confuses the DE which usually changes the
display configuration and messes up a dual-screen setup).
This patch gives the handlers the chance to examine the event and
block the keypress if the event is device specific.
v2: refactor as suggested by Zhang Rui <rui.zhang@intel.com>

Signed-off-by: Luca Tettamanti <kronos.it@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/acpi/video.c

@@ -1448,8 +1448,7 @@ static void acpi_video_bus_notify(struct acpi_device *device, u32 event)
 	case ACPI_VIDEO_NOTIFY_SWITCH:	/* User requested a switch,
 					 * most likely via hotkey. */
 		acpi_bus_generate_proc_event(device, event, 0);
-		if (!acpi_notifier_call_chain(device, event, 0))
-			keycode = KEY_SWITCHVIDEOMODE;
+		keycode = KEY_SWITCHVIDEOMODE;
 		break;
 
 	case ACPI_VIDEO_NOTIFY_PROBE:	/* User plugged in or removed a video
@@ -1479,8 +1478,9 @@ static void acpi_video_bus_notify(struct acpi_device *device, u32 event)
 		break;
 	}
 
-	if (event != ACPI_VIDEO_NOTIFY_SWITCH)
-		acpi_notifier_call_chain(device, event, 0);
+	if (acpi_notifier_call_chain(device, event, 0))
+		/* Something vetoed the keypress. */
+		keycode = 0;
 
 	if (keycode) {
 		input_report_key(input, keycode, 1);