HID: multitouch: Properly deal with Win8 PTP reports with 0 touches

The Windows Precision Touchpad spec "Figure 4 Button Only Down and Up"
and "Table 9 Report Sequence for Button Only Down and Up" indicate
that the first packet of a (possibly hybrid mode multi-packet) frame
may contain a contact-count of 0 if only a button is pressed and no
fingers are detected.

This means that a value of 0 for contact-count is a valid value and
should be used as expected contact count when it is the first packet
(num_received == 0), as extra check to make sure that this is the first
packet of a buttons only frame, we also check that the timestamp is
different.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 30 insertions, 2 deletions

diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index 9ef24b518f12..d8b1cad74faf 100644
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -119,6 +119,9 @@ 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 scantime_index;     /* scantime field index in the report */
+        int scantime_val_index; /* scantime value index in the field */
+        int prev_scantime;      /* scantime reported in the previous packet */
         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 */
@@ -599,6 +602,12 @@ static int mt_touch_input_mapping(struct hid_device *hdev, struct hid_input *hi,
                                 EV_MSC, MSC_TIMESTAMP);
                         input_set_capability(hi->input, EV_MSC, MSC_TIMESTAMP);
                         mt_store_field(usage, td, hi);
+                        /* Ignore if indexes are out of bounds. */
+                        if (field->index >= field->report->maxfield ||
+                            usage->usage_index >= field->report_count)
+                                return 1;
+                        td->scantime_index = field->index;
+                        td->scantime_val_index = usage->usage_index;
                         return 1;
                 case HID_DG_CONTACTCOUNT:
                         /* Ignore if indexes are out of bounds. */
@@ -855,9 +864,10 @@ static void mt_process_mt_event(struct hid_device *hid, struct hid_field *field,
 static void mt_touch_report(struct hid_device *hid, struct hid_report *report)
 {
         struct mt_device *td = hid_get_drvdata(hid);
+        __s32 cls = td->mtclass.name;
         struct hid_field *field;
         unsigned count;
-        int r, n;
+        int r, n, scantime = 0;
 
         /* sticky fingers release in progress, abort */
         if (test_and_set_bit(MT_IO_FLAGS_RUNNING, &td->mt_io_flags))
@@ -867,12 +877,29 @@ static void mt_touch_report(struct hid_device *hid, struct hid_report *report)
          * Includes multi-packet support where subsequent
          * packets are sent with zero contactcount.
          */
+        if (td->scantime_index >= 0) {
+                field = report->field[td->scantime_index];
+                scantime = field->value[td->scantime_val_index];
+        }
         if (td->cc_index >= 0) {
                 struct hid_field *field = report->field[td->cc_index];
                 int value = field->value[td->cc_value_index];
-                if (value)
+
+                /*
+                 * For Win8 PTPs the first packet (td->num_received == 0) may
+                 * have a contactcount of 0 if there only is a button event.
+                 * We double check that this is not a continuation packet
+                 * of a possible multi-packet frame be checking that the
+                 * timestamp has changed.
+                 */
+                if ((cls == MT_CLS_WIN_8 || cls == MT_CLS_WIN_8_DUAL) &&
+                    td->num_received == 0 && td->prev_scantime != scantime)
+                        td->num_expected = value;
+                /* A non 0 contact count always indicates a first packet */
+                else if (value)
                         td->num_expected = value;
         }
+        td->prev_scantime = scantime;
 
         for (r = 0; r < report->maxfield; r++) {
                 field = report->field[r];
@@ -1329,6 +1356,7 @@ static int mt_probe(struct hid_device *hdev, const struct hid_device_id *id)
         td->maxcontact_report_id = -1;
         td->inputmode_value = MT_INPUTMODE_TOUCHSCREEN;
         td->cc_index = -1;
+        td->scantime_index = -1;
         td->mt_report_id = -1;
         hid_set_drvdata(hdev, td);