The previous implementation introduced a randomness in the splitting
of the different touches reported by the device. This version is more
robust as we don't rely on hi->input->absbit, but on our own structure.

This also prepares hid-multitouch to better support Win8 devices.

Signed-off-by: Benjamin Tissoires <redacted>
---
 drivers/hid/hid-multitouch.c |   58 +++++++++++++++++++++++++++++++++--------
 1 files changed, 46 insertions(+), 12 deletions(-)

diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index 84bb32e..c6ffb05 100644
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c

@@ -70,9 +70,16 @@ struct mt_class {
 	bool is_indirect;	/* true for touchpads */
 };
 
+struct mt_fields {
+	unsigned usages[HID_MAX_FIELDS];
+	unsigned int length;
+};
+
 struct mt_device {
 	struct mt_slot curdata;	/* placeholder of incoming data */
 	struct mt_class mtclass;	/* our mt device class */
+	struct mt_fields *fields;	/* temporary placeholder for storing the
+					   multitouch fields */

 	unsigned last_field_index;	/* last field index of the report */
 	unsigned last_slot_field;	/* the last field of a slot */
 	__s8 inputmode;		/* InputMode HID feature, -1 if non-existent */

@@ -275,11 +282,15 @@ static void set_abs(struct input_dev *input, unsigned int code,
 	input_set_abs_params(input, code, fmin, fmax, fuzz, 0);
 }
 
-static void set_last_slot_field(struct hid_usage *usage, struct mt_device *td,
+static void mt_store_field(struct hid_usage *usage, struct mt_device *td,
 		struct hid_input *hi)

+
+	if (f->length >= HID_MAX_FIELDS)
+		return;
+
+	f->usages[f->length++] = usage->hid;
 }
 
 static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,

@@ -330,7 +341,7 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 				cls->sn_move);
 			/* touchscreen emulation */
 			set_abs(hi->input, ABS_X, field, cls->sn_move);
-			set_last_slot_field(usage, td, hi);
+			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			return 1;
 		case HID_GD_Y:

@@ -340,7 +351,7 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 				cls->sn_move);
 			/* touchscreen emulation */
 			set_abs(hi->input, ABS_Y, field, cls->sn_move);
-			set_last_slot_field(usage, td, hi);
+			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			return 1;
 		}

@@ -349,24 +360,24 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 	case HID_UP_DIGITIZER:
 		switch (usage->hid) {
 		case HID_DG_INRANGE:
-			set_last_slot_field(usage, td, hi);
+			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			return 1;
 		case HID_DG_CONFIDENCE:
-			set_last_slot_field(usage, td, hi);
+			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			return 1;
 		case HID_DG_TIPSWITCH:
 			hid_map_usage(hi, usage, bit, max, EV_KEY, BTN_TOUCH);
 			input_set_capability(hi->input, EV_KEY, BTN_TOUCH);
-			set_last_slot_field(usage, td, hi);
+			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			return 1;
 		case HID_DG_CONTACTID:
 			if (!td->maxcontacts)
 				td->maxcontacts = MT_DEFAULT_MAXCONTACT;
 			input_mt_init_slots(hi->input, td->maxcontacts);
-			td->last_slot_field = usage->hid;
+			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			td->touches_by_report++;
 			return 1;

@@ -375,7 +386,7 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 					EV_ABS, ABS_MT_TOUCH_MAJOR);
 			set_abs(hi->input, ABS_MT_TOUCH_MAJOR, field,
 				cls->sn_width);
-			set_last_slot_field(usage, td, hi);
+			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			return 1;
 		case HID_DG_HEIGHT:

@@ -385,7 +396,7 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 				cls->sn_height);
 			input_set_abs_params(hi->input,
 					ABS_MT_ORIENTATION, 0, 1, 0, 0);
-			set_last_slot_field(usage, td, hi);
+			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			return 1;
 		case HID_DG_TIPPRESSURE:

@@ -396,7 +407,7 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 			/* touchscreen emulation */
 			set_abs(hi->input, ABS_PRESSURE, field,
 				cls->sn_pressure);
-			set_last_slot_field(usage, td, hi);
+			mt_store_field(usage, td, hi);
 			td->last_field_index = field->index;
 			return 1;
 		case HID_DG_CONTACTCOUNT:

@@ -650,6 +661,16 @@ static void mt_post_parse_default_settings(struct mt_device *td)
 	td->mtclass.quirks = quirks;
 }
 
+static void mt_post_parse(struct mt_device *td)
+{
+	struct mt_fields *f = td->fields;
+
+	if (td->touches_by_report > 0) {
+		int field_count_per_touch = f->length / td->touches_by_report;
+		td->last_slot_field = f->usages[field_count_per_touch - 1]->hid;
+	}
+}
+
 static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 {
 	int ret, i;

@@ -680,6 +701,13 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	td->maxcontact_report_id = -1;
 	hid_set_drvdata(hdev, td);
 
+	td->fields = kzalloc(sizeof(struct mt_fields), GFP_KERNEL);
+	if (!td->fields) {
+		dev_err(&hdev->dev, "cannot allocate multitouch fields data\n");
+		ret = -ENOMEM;
+		goto fail;
+	}
+

 	ret = hid_parse(hdev);
 	if (ret != 0)
 		goto fail;

@@ -688,6 +716,8 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	if (ret)
 		goto fail;
 
+	mt_post_parse(td);
+
 	if (id->vendor == HID_ANY_ID && id->product == HID_ANY_ID)
 		mt_post_parse_default_settings(td);
 

@@ -705,9 +735,13 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	mt_set_maxcontacts(hdev);
 	mt_set_input_mode(hdev);
 
+	kfree(td->fields);
+	td->fields = NULL;
+