Input: wacom - use full 32-bit HID Usage value in switch statement

A HID Usage is a 32-bit value: an upper 16-bit "page" and a lower 16-bit
ID. While the two halves are normally reported seperately, only the
combination uniquely idenfifes a particular HID Usage.

The existing code performs the comparison in two steps, first performing a
switch on the ID and then verifying the page within each case. While this
works fine, it is very akward to handle two Usages that share a single ID,
such as HID_USAGE_PRESSURE and HID_USAGE_X because the case statement can
only have a single identifier.

To work around this, we now check the full 32-bit HID Usage directly rather
than first checking the ID and then the page.  This allows the switch
statement to have distinct cases for e.g. HID_USAGE_PRESSURE and
HID_USAGE_X.
Signed-off-by: Jason Gerecke <killertofu@gmail.com>
Tested-by: Aaron Skomra <Aaron.Skomra@wacom.com>
Reviewed-by: Carl Worth <cworth@cworth.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/tablet/wacom_sys.c

@@ -22,23 +22,17 @@
 #define HID_USAGE_PAGE_DIGITIZER	0x0d
 #define HID_USAGE_PAGE_DESKTOP		0x01
 #define HID_USAGE			0x09
-#define HID_USAGE_X			0x30
-#define HID_USAGE_Y			0x31
-#define HID_USAGE_X_TILT		0x3d
-#define HID_USAGE_Y_TILT		0x3e
-#define HID_USAGE_FINGER		0x22
-#define HID_USAGE_STYLUS		0x20
-#define HID_USAGE_CONTACTMAX		0x55
+#define HID_USAGE_X			((HID_USAGE_PAGE_DESKTOP << 16) | 0x30)
+#define HID_USAGE_Y			((HID_USAGE_PAGE_DESKTOP << 16) | 0x31)
+#define HID_USAGE_X_TILT		((HID_USAGE_PAGE_DIGITIZER << 16) | 0x3d)
+#define HID_USAGE_Y_TILT		((HID_USAGE_PAGE_DIGITIZER << 16) | 0x3e)
+#define HID_USAGE_FINGER		((HID_USAGE_PAGE_DIGITIZER << 16) | 0x22)
+#define HID_USAGE_STYLUS		((HID_USAGE_PAGE_DIGITIZER << 16) | 0x20)
+#define HID_USAGE_CONTACTMAX		((HID_USAGE_PAGE_DIGITIZER << 16) | 0x55)
 #define HID_COLLECTION			0xa1
 #define HID_COLLECTION_LOGICAL		0x02
 #define HID_COLLECTION_END		0xc0
 
-enum {
-	WCM_UNDEFINED = 0,
-	WCM_DESKTOP,
-	WCM_DIGITIZER,
-};
-
 struct hid_descriptor {
 	struct usb_descriptor_header header;
 	__le16   bcdHID;
@@ -305,7 +299,7 @@ static int wacom_parse_hid(struct usb_interface *intf,
 	char limit = 0;
 	/* result has to be defined as int for some devices */
 	int result = 0, touch_max = 0;
-	int i = 0, usage = WCM_UNDEFINED, finger = 0, pen = 0;
+	int i = 0, page = 0, finger = 0, pen = 0;
 	unsigned char *report;
 
 	report = kzalloc(hid_desc->wDescriptorLength, GFP_KERNEL);
@@ -332,23 +326,13 @@ static int wacom_parse_hid(struct usb_interface *intf,
 
 		switch (report[i]) {
 		case HID_USAGE_PAGE:
-			switch (report[i + 1]) {
-			case HID_USAGE_PAGE_DIGITIZER:
-				usage = WCM_DIGITIZER;
+			page = report[i + 1];
 			i++;
 			break;
 
-			case HID_USAGE_PAGE_DESKTOP:
-				usage = WCM_DESKTOP;
-				i++;
-				break;
-			}
-			break;
-
 		case HID_USAGE:
-			switch (report[i + 1]) {
+			switch (page << 16 | report[i + 1]) {
 			case HID_USAGE_X:
-				if (usage == WCM_DESKTOP) {
 				if (finger) {
 					features->device_type = BTN_TOOL_FINGER;
 					/* touch device at least supports one touch point */
@@ -414,11 +398,9 @@ static int wacom_parse_hid(struct usb_interface *intf,
 						get_unaligned_le16(&report[i + 3]);
 					i += 4;
 				}
-				}
 				break;
 
 			case HID_USAGE_Y:
-				if (usage == WCM_DESKTOP) {
 				if (finger) {
 					switch (features->type) {
 					case TABLETPC2FG:
@@ -460,7 +442,6 @@ static int wacom_parse_hid(struct usb_interface *intf,
 						get_unaligned_le16(&report[i + 3]);
 					i += 4;
 				}
-				}
 				break;
 
 			case HID_USAGE_FINGER:
@@ -489,7 +470,7 @@ static int wacom_parse_hid(struct usb_interface *intf,
 
 		case HID_COLLECTION_END:
 			/* reset UsagePage and Finger */
-			finger = usage = 0;
+			finger = page = 0;
 			break;
 
 		case HID_COLLECTION: