[PATCH 1/2] HID: multitouch: report MT_TOOL_PALM for non-confident touches

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

According to Microsoft specification [1] for Precision Touchpads (and
Touchscreens) the devices use "confidence" reports to signal accidental
touches, or contacts that are "too large to be a finger". Instead of
simply marking contact inactive in this case (which causes issues if
contact was originally proper and we lost confidence in it later, as
this results in accidental clicks, drags, etc), let's report such
contacts as MT_TOOL_PALM and let userspace decide what to do.
Additionally, let's report contact size for such touches as maximum
allowed for major/minor, which should help userspace that is not yet
aware of MT_TOOL_PALM to still perform palm rejection.

An additional complication, is that some firmwares do not report
non-confident touches as active. To cope with this we delay release of
such contact (i.e. if contact was active we first report it as still
active MT+TOOL_PALM and then synthesize the release event in a separate
frame).

[1] https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/touchpad-windows-precision-touchpad-collection

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/hid/hid-multitouch.c | 86 +++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 77 insertions(+), 9 deletions(-)

diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index 440b999304a5..c28defe50a10 100644
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -114,6 +114,8 @@ struct mt_device {
 	struct timer_list release_timer;	/* to release sticky fingers */
 	struct mt_fields *fields;	/* temporary placeholder for storing the
 					   multitouch fields */
+	unsigned long *pending_palm_slots; /* slots where we reported palm
+						and need to release */
 	unsigned long mt_io_flags;	/* mt flags (MT_IO_FLAGS_*) */
 	int cc_index;	/* contact count field index in the report */
 	int cc_value_index;	/* contact count value index in the field */
@@ -543,8 +545,12 @@ static int mt_touch_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 		case HID_DG_CONFIDENCE:
 			if ((cls->name == MT_CLS_WIN_8 ||
 				cls->name == MT_CLS_WIN_8_DUAL) &&
-				field->application == HID_DG_TOUCHPAD)
+			    field->application == HID_DG_TOUCHPAD) {
 				cls->quirks |= MT_QUIRK_CONFIDENCE;
+				input_set_abs_params(hi->input,
+					ABS_MT_TOOL_TYPE,
+					MT_TOOL_FINGER, MT_TOOL_PALM, 0, 0);
+			}
 			mt_store_field(usage, td, hi);
 			return 1;
 		case HID_DG_TIPSWITCH:
@@ -657,6 +663,7 @@ static void mt_complete_slot(struct mt_device *td, struct input_dev *input)
 
 	if (td->curvalid || (td->mtclass.quirks & MT_QUIRK_ALWAYS_VALID)) {
 		int active;
+		int tool;
 		int slotnum = mt_compute_slot(td, input);
 		struct mt_slot *s = &td->curdata;
 		struct input_mt *mt = input->mt;
@@ -671,24 +678,56 @@ static void mt_complete_slot(struct mt_device *td, struct input_dev *input)
 				return;
 		}
 
+		active = s->touch_state || s->inrange_state;
+
 		if (!(td->mtclass.quirks & MT_QUIRK_CONFIDENCE))
 			s->confidence_state = 1;
-		active = (s->touch_state || s->inrange_state) &&
-							s->confidence_state;
+
+		if (likely(s->confidence_state)) {
+			tool = MT_TOOL_FINGER;
+		} else {
+			tool = MT_TOOL_PALM;
+			if (!active &&
+			    input_mt_is_active(&mt->slots[slotnum])) {
+				/*
+				 * The non-confidence was reported for
+				 * previously valid contact that is also no
+				 * longer valid. We can't simply report
+				 * lift-off as userspace will not be aware
+				 * of non-confidence, so we need to split
+				 * it into 2 events: active MT_TOOL_PALM
+				 * and a separate liftoff.
+				 */
+				active = true;
+				set_bit(slotnum, td->pending_palm_slots);
+			}
+		}
 
 		input_mt_slot(input, slotnum);
-		input_mt_report_slot_state(input, MT_TOOL_FINGER, active);
+		input_mt_report_slot_state(input, tool, active);
 		if (active) {
 			/* this finger is in proximity of the sensor */
 			int wide = (s->w > s->h);
 			int major = max(s->w, s->h);
 			int minor = min(s->w, s->h);
 
-			/*
-			 * divided by two to match visual scale of touch
-			 * for devices with this quirk
-			 */
-			if (td->mtclass.quirks & MT_QUIRK_TOUCH_SIZE_SCALING) {
+			if (unlikely(!s->confidence_state)) {
+				/*
+				 * When reporting palm, set contact to maximum
+				 * size to help userspace that does not
+				 * recognize MT_TOOL_PALM to reject contacts
+				 * that are too large.
+				 */
+				major = input_abs_get_max(input,
+							  ABS_MT_TOUCH_MAJOR);
+				minor = input_abs_get_max(input,
+							  ABS_MT_TOUCH_MINOR);
+			} else if (td->mtclass.quirks &
+					MT_QUIRK_TOUCH_SIZE_SCALING) {
+				/*
+				 * divided by two to match visual scale of touch
+				 * for devices with this quirk
+				 */
 				major = major >> 1;
 				minor = minor >> 1;
 			}
@@ -711,6 +750,25 @@ static void mt_complete_slot(struct mt_device *td, struct input_dev *input)
 	td->num_received++;
 }
 
+static void mt_release_pending_palms(struct mt_device *td,
+				     struct input_dev *input)
+{
+	int slotnum;
+	bool need_sync = false;
+
+	for_each_set_bit(slotnum, td->pending_palm_slots, td->maxcontacts) {
+		clear_bit(slotnum, td->pending_palm_slots);
+
+		input_mt_slot(input, slotnum);
+		input_mt_report_slot_state(input, MT_TOOL_PALM, false);
+
+		need_sync = true;
+	}
+
+	if (need_sync)
+		input_sync(input);
+}
+
 /*
  * this function is called when a whole packet has been received and processed,
  * so that it can decide what to send to the input layer.
@@ -719,6 +777,9 @@ static void mt_sync_frame(struct mt_device *td, struct input_dev *input)
 {
 	input_mt_sync_frame(input);
 	input_sync(input);
+
+	mt_release_pending_palms(td, input);
+
 	td->num_received = 0;
 	if (test_bit(MT_IO_FLAGS_ACTIVE_SLOTS, &td->mt_io_flags))
 		set_bit(MT_IO_FLAGS_PENDING_SLOTS, &td->mt_io_flags);
@@ -903,6 +964,13 @@ static int mt_touch_input_configured(struct hid_device *hdev,
 	if (td->is_buttonpad)
 		__set_bit(INPUT_PROP_BUTTONPAD, input->propbit);
 
+	td->pending_palm_slots = devm_kcalloc(&hi->input->dev,
+					      BITS_TO_LONGS(td->maxcontacts),
+					      sizeof(long),
+					      GFP_KERNEL);
+	if (!td->pending_palm_slots)
+		return -ENOMEM;
+
 	ret = input_mt_init_slots(input, td->maxcontacts, td->mt_flags);
 	if (ret)
 		return ret;
-- 
2.14.0.434.g98096fd7a8-goog