HID: multitouch: fix LG Melfas touchscreen

The LG Melfas touchscreen has a bad firmware where it declares the Contact ID
field as constant while it shouldn't. This messes up the autodetection and the
reporting of the events by hid-multitouch given that hid-input ignores constant
fields.

The autodetection is simply worked around by manually adding the device to
hid_have_special_driver[].

The processing of the events requires either a report fixup, or some specific
case handling. Given that the report fixup would require to basically rewrite
all the report descriptor, I went for the programatic way of fixing that after
the report descriptors are loaded.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1416181
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-core.c

@@ -1933,6 +1933,7 @@ static const struct hid_device_id hid_have_special_driver[] = {
 	{ HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_LENOVO, USB_DEVICE_ID_LENOVO_CBTKBD) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_LENOVO, USB_DEVICE_ID_LENOVO_TPPRODOCK) },
 #endif
+	{ HID_USB_DEVICE(USB_VENDOR_ID_LG, USB_DEVICE_ID_LG_MELFAS_MT) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_LOGITECH, USB_DEVICE_ID_MX3000_RECEIVER) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_LOGITECH, USB_DEVICE_ID_S510_RECEIVER) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_LOGITECH, USB_DEVICE_ID_S510_RECEIVER_2) },

drivers/hid/hid-ids.h

@@ -633,6 +633,7 @@
 
 #define USB_VENDOR_ID_LG		0x1fd2
 #define USB_DEVICE_ID_LG_MULTITOUCH	0x0064
+#define USB_DEVICE_ID_LG_MELFAS_MT	0x6007
 
 #define USB_VENDOR_ID_LOGITECH		0x046d
 #define USB_DEVICE_ID_LOGITECH_AUDIOHUB 0x0a0e

drivers/hid/hid-multitouch.c

@@ -68,6 +68,7 @@ MODULE_LICENSE("GPL");
 #define MT_QUIRK_HOVERING		(1 << 11)
 #define MT_QUIRK_CONTACT_CNT_ACCURATE	(1 << 12)
 #define MT_QUIRK_FORCE_GET_FEATURE	(1 << 13)
+#define MT_QUIRK_FIX_CONST_CONTACT_ID	(1 << 14)
 
 #define MT_INPUTMODE_TOUCHSCREEN	0x02
 #define MT_INPUTMODE_TOUCHPAD		0x03
@@ -157,6 +158,7 @@ static void mt_post_parse(struct mt_device *td);
 #define MT_CLS_FLATFROG				0x0107
 #define MT_CLS_GENERALTOUCH_TWOFINGERS		0x0108
 #define MT_CLS_GENERALTOUCH_PWT_TENFINGERS	0x0109
+#define MT_CLS_LG				0x010a
 #define MT_CLS_VTL				0x0110
 
 #define MT_DEFAULT_MAXCONTACT	10
@@ -263,6 +265,12 @@ static struct mt_class mt_classes[] = {
 		.sn_move = 2048,
 		.maxcontacts = 40,
 	},
+	{ .name = MT_CLS_LG,
+		.quirks = MT_QUIRK_ALWAYS_VALID |
+			MT_QUIRK_FIX_CONST_CONTACT_ID |
+			MT_QUIRK_IGNORE_DUPLICATES |
+			MT_QUIRK_HOVERING |
+			MT_QUIRK_CONTACT_CNT_ACCURATE },
 	{ .name = MT_CLS_VTL,
 		.quirks = MT_QUIRK_ALWAYS_VALID |
 			MT_QUIRK_CONTACT_CNT_ACCURATE |
@@ -1078,6 +1086,34 @@ static int mt_input_configured(struct hid_device *hdev, struct hid_input *hi)
 	return 0;
 }
 
+static void mt_fix_const_field(struct hid_field *field, unsigned int usage)
+{
+	if (field->usage[0].hid != usage ||
+	    !(field->flags & HID_MAIN_ITEM_CONSTANT))
+		return;
+
+	field->flags &= ~HID_MAIN_ITEM_CONSTANT;
+	field->flags |= HID_MAIN_ITEM_VARIABLE;
+}
+
+static void mt_fix_const_fields(struct hid_device *hdev, unsigned int usage)
+{
+	struct hid_report *report;
+	int i;
+
+	list_for_each_entry(report,
+			    &hdev->report_enum[HID_INPUT_REPORT].report_list,
+			    list) {
+
+		if (!report->maxfield)
+			continue;
+
+		for (i = 0; i < report->maxfield; i++)
+			if (report->field[i]->maxusage >= 1)
+				mt_fix_const_field(report->field[i], usage);
+	}
+}
+
 static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 {
 	int ret, i;
@@ -1151,6 +1187,9 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	if (ret != 0)
 		return ret;
 
+	if (mtclass->quirks & MT_QUIRK_FIX_CONST_CONTACT_ID)
+		mt_fix_const_fields(hdev, HID_DG_CONTACTID);
+
 	ret = hid_hw_start(hdev, HID_CONNECT_DEFAULT);
 	if (ret)
 		return ret;
@@ -1398,6 +1437,11 @@ static const struct hid_device_id mt_devices[] = {
 		MT_USB_DEVICE(USB_VENDOR_ID_ILITEK,
 			USB_DEVICE_ID_ILITEK_MULTITOUCH) },
 
+	/* LG Melfas panel */
+	{ .driver_data = MT_CLS_LG,
+		HID_USB_DEVICE(USB_VENDOR_ID_LG,
+			USB_DEVICE_ID_LG_MELFAS_MT) },
+
 	/* MosArt panels */
 	{ .driver_data = MT_CLS_CONFIDENCE_MINUS_ONE,
 		MT_USB_DEVICE(USB_VENDOR_ID_ASUS,