HID: hid-logitech: Compute combined pedals value

Add support for computing a combined accelerator/brake axis for wheels
which don't contain combined data in their HID stream.

This includes DFGT, G25, G27, G29 and Wii-Wheel.
Signed-off-by: NSimon Wood <simon@mungewell.org>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/hid-lg4ff.c

@@ -332,6 +332,7 @@ int lg4ff_adjust_input_event(struct hid_device *hid, struct hid_field *field,
 int lg4ff_raw_event(struct hid_device *hdev, struct hid_report *report,
 		u8 *rd, int size, struct lg_drv_data *drv_data)
 {
+	int offset;
 	struct lg4ff_device_entry *entry = drv_data->device_props;
 
 	if (!entry)
@@ -353,9 +354,25 @@ int lg4ff_raw_event(struct hid_device *hdev, struct hid_report *report,
 			rd[5] = rd[4];
 			rd[6] = 0x7F;
 			return 1;
+		case USB_DEVICE_ID_LOGITECH_G25_WHEEL:
+		case USB_DEVICE_ID_LOGITECH_G27_WHEEL:
+			offset = 5;
+			break;
+		case USB_DEVICE_ID_LOGITECH_DFGT_WHEEL:
+		case USB_DEVICE_ID_LOGITECH_G29_WHEEL:
+			offset = 6;
+			break;
+		case USB_DEVICE_ID_LOGITECH_WII_WHEEL:
+			offset = 3;
+			break;
 		default:
 			return 0;
 		}
+
+		/* Compute a combined axis when wheel does not supply it */
+		rd[offset] = (0xFF + rd[offset] - rd[offset+1]) >> 1;
+		rd[offset+1] = 0x7F;
+		return 1;
 	}
 
 	return 0;