HID: hid-elo: some systems cannot stomach work around

Some systems although they have firmware class 'M', which usually
needs a work around to not crash, must not be subjected to the
work around because the work around crashes them. They cannot be
told apart by their own device descriptor, but as they are part
of compound devices, can be identified by looking at their siblings.
Signed-off-by: NOliver Neukum <oneukum@suse.de>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/hid-elo.c

@@ -181,7 +181,40 @@ static void elo_work(struct work_struct *work)
  */
 static bool elo_broken_firmware(struct usb_device *dev)
 {
-	return use_fw_quirk && le16_to_cpu(dev->descriptor.bcdDevice) == 0x10d;
+	struct usb_device *hub = dev->parent;
+	struct usb_device *child = NULL;
+	u16 fw_lvl = le16_to_cpu(dev->descriptor.bcdDevice);
+	u16 child_vid, child_pid;
+	int i;
+    
+	if (!use_fw_quirk)
+		return false;
+	if (fw_lvl != 0x10d)
+		return false;
+
+	/* iterate sibling devices of the touch controller */
+	usb_hub_for_each_child(hub, i, child) {
+		child_vid = le16_to_cpu(child->descriptor.idVendor);
+		child_pid = le16_to_cpu(child->descriptor.idProduct);
+
+		/*
+		 * If one of the devices below is present attached as a sibling of 
+		 * the touch controller then  this is a newer IBM 4820 monitor that 
+		 * does not need the IBM-requested workaround if fw level is
+		 * 0x010d - aka 'M'.
+		 * No other HW can have this combination.
+		 */
+		if (child_vid==0x04b3) {
+			switch (child_pid) {
+			case 0x4676: /* 4820 21x Video */
+			case 0x4677: /* 4820 51x Video */
+			case 0x4678: /* 4820 2Lx Video */
+			case 0x4679: /* 4820 5Lx Video */
+				return false;
+			}
+		}
+	}
+	return true;
 }
 
 static int elo_probe(struct hid_device *hdev, const struct hid_device_id *id)