[PATCH v2 3/3] HID: multitouch: Fix BTN_LEFT on some touchpads

[Hans de Goede <hdegoede@redhat.com>]

This commit fixes 2 different issues with BTN_LEFT on touchpads in one go:

1) Devices in "single finger hybrid mode" will send one report per finger,
   on some devices only the first report of such a multi-packet frame will
   contain a value for BTN_LEFT, in subsequent reports (if multiple fingers
   are down) the value is always 0, causing hid-mt to report BTN_LEFT going
   1 - 0 - 1 - 0 when pressing a clickpad and putting down a second finger.
   This happens for example on USB 0603:0002 mt touchpads.

2) According to the Win8 Precision Touchpad spec, inside the HID_UP_BUTTON
   usage-page usage 1 is for a clickpad getting clicked, 2 for an external
   left button and 3 for an external right button. Since Linux uses
   BTN_LEFT for a clickpad being clicked we end up mapping both usage 1
   and 2 to BTN_LEFT and if a single report contains both then we ended
   up always reporting the value of both in a single SYN, e.g. :
   BTN_LEFT 1, BTN_LEFT 0, SYN. This happens for example with SYNA3602
   i2c mt touchpads.

This commit fixes both issues by not immediately reporting BTN_LEFT when
we parse the report, but instead or-ing the values of all fields mapped
to BTN_LEFT together and reporting the result from mt_sync_frame()
when we've a complete frame.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Changes in v2:
-Rewrite of v1 of "HID: multitouch: Fix BTN_LEFT 0-1-0-1 events on Novatek
 mt touchpad" to kill two birds with one stone
---
 drivers/hid/hid-multitouch.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index 76a3e9e074ba..bacbd1ba75ba 100644
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -117,6 +117,7 @@ struct mt_device {
 	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 */
+	int btn_left;		/* BTN_LEFT state */
 	unsigned last_slot_field;	/* the last field of a slot */
 	unsigned mt_report_id;	/* the report ID of the multitouch device */
 	unsigned long initial_quirks;	/* initial quirks state */
@@ -717,9 +718,11 @@ static void mt_complete_slot(struct mt_device *td, struct input_dev *input)
  */
 static void mt_sync_frame(struct mt_device *td, struct input_dev *input)
 {
+	input_event(input, EV_KEY, BTN_LEFT, td->btn_left);
 	input_mt_sync_frame(input);
 	input_sync(input);
 	td->num_received = 0;
+	td->btn_left = 0;
 	if (test_bit(MT_IO_FLAGS_ACTIVE_SLOTS, &td->mt_io_flags))
 		set_bit(MT_IO_FLAGS_PENDING_SLOTS, &td->mt_io_flags);
 	else
@@ -794,6 +797,17 @@ static void mt_process_mt_event(struct hid_device *hid, struct hid_field *field,
 			break;
 
 		default:
+			/*
+			 * On some hardware we get multiple BTN_LEFT reports
+			 * per frame, with only 1 report reporting 1 if pressed.
+			 * So for BTN_LEFT we or the values together and
+			 * report the combined state in mt_sync_frame()
+			 */
+			if (usage->type == EV_KEY && usage->code == BTN_LEFT) {
+				td->btn_left |= value;
+				return;
+			}
+
 			if (usage->type)
 				input_event(input, usage->type, usage->code,
 						value);
-- 
2.14.3