HID: hid-multitouch: forward MSC_TIMESTAMP

Computes and forwards the device timestamp according to the specification.

Many devices use a 16-bit timestamp field, with a resolution of 100us,
therefore rolling around very frequently (every 6.5 seconds). To make sure
there is no ambiguity, the timestamp reported to the input stack reset to
0 whenever the time between 2 received events is greater than
MAX_TIMESTAMP_INTERVAL (1 second).

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Acked-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

2 files changed, 43 insertions, 0 deletions

diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index 440b999304a5..996bdc9bf0e5 100644
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -43,6 +43,7 @@
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/input/mt.h>
+#include <linux/jiffies.h>
 #include <linux/string.h>
 #include <linux/timer.h>
 
@@ -136,6 +137,9 @@ struct mt_device {
         bool serial_maybe;      /* need to check for serial protocol */
         bool curvalid;          /* is the current contact valid? */
         unsigned mt_flags;      /* flags to pass to input-mt */
+        __s32 dev_time;         /* the scan time provided by the device */
+        unsigned long jiffies;  /* the frame's jiffies */
+        int timestamp;          /* the timestamp to be sent */
 };
 
 static void mt_post_parse_default_settings(struct mt_device *td);
@@ -177,6 +181,12 @@ static void mt_post_parse(struct mt_device *td);
 #define MT_DEFAULT_MAXCONTACT   10
 #define MT_MAX_MAXCONTACT       250
 
+/*
+ * Resync device and local timestamps after that many microseconds without
+ * receiving data.
+ */
+#define MAX_TIMESTAMP_INTERVAL  1000000
+
 #define MT_USB_DEVICE(v, p)     HID_DEVICE(BUS_USB, HID_GROUP_MULTITOUCH, v, p)
 #define MT_BT_DEVICE(v, p)      HID_DEVICE(BUS_BLUETOOTH, HID_GROUP_MULTITOUCH, v, p)
 
@@ -583,6 +593,12 @@ static int mt_touch_input_mapping(struct hid_device *hdev, struct hid_input *hi,
                                 cls->sn_pressure);
                         mt_store_field(usage, td, hi);
                         return 1;
+                case HID_DG_SCANTIME:
+                        hid_map_usage(hi, usage, bit, max,
+                                EV_MSC, MSC_TIMESTAMP);
+                        input_set_capability(hi->input, EV_MSC, MSC_TIMESTAMP);
+                        mt_store_field(usage, td, hi);
+                        return 1;
                 case HID_DG_CONTACTCOUNT:
                         /* Ignore if indexes are out of bounds. */
                         if (field->index >= field->report->maxfield ||
@@ -718,6 +734,7 @@ 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_mt_sync_frame(input);
+        input_event(input, EV_MSC, MSC_TIMESTAMP, td->timestamp);
         input_sync(input);
         td->num_received = 0;
         if (test_bit(MT_IO_FLAGS_ACTIVE_SLOTS, &td->mt_io_flags))
@@ -727,6 +744,28 @@ static void mt_sync_frame(struct mt_device *td, struct input_dev *input)
         clear_bit(MT_IO_FLAGS_ACTIVE_SLOTS, &td->mt_io_flags);
 }
 
+static int mt_compute_timestamp(struct mt_device *td, struct hid_field *field,
+                __s32 value)
+{
+        long delta = value - td->dev_time;
+        unsigned long jdelta = jiffies_to_usecs(jiffies - td->jiffies);
+
+        td->jiffies = jiffies;
+        td->dev_time = value;
+
+        if (delta < 0)
+                delta += field->logical_maximum;
+
+        /* HID_DG_SCANTIME is expressed in 100us, we want it in us. */
+        delta *= 100;
+
+        if (jdelta > MAX_TIMESTAMP_INTERVAL)
+                /* No data received for a while, resync the timestamp. */
+                return 0;
+        else
+                return td->timestamp + delta;
+}
+
 static int mt_touch_event(struct hid_device *hid, struct hid_field *field,
                                 struct hid_usage *usage, __s32 value)
 {
@@ -787,6 +826,9 @@ static void mt_process_mt_event(struct hid_device *hid, struct hid_field *field,
                 case HID_DG_HEIGHT:
                         td->curdata.h = value;
                         break;
+                case HID_DG_SCANTIME:
+                        td->timestamp = mt_compute_timestamp(td, field, value);
+                        break;
                 case HID_DG_CONTACTCOUNT:
                         break;
                 case HID_DG_TOUCH:
diff --git a/include/linux/hid.h b/include/linux/hid.h
index ab05a86269dc..47dd962d9a7a 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -289,6 +289,7 @@ struct hid_item {
 #define HID_DG_DEVICEINDEX      0x000d0053
 #define HID_DG_CONTACTCOUNT     0x000d0054
 #define HID_DG_CONTACTMAX       0x000d0055
+#define HID_DG_SCANTIME         0x000d0056
 #define HID_DG_BUTTONTYPE       0x000d0059
 #define HID_DG_BARRELSWITCH2    0x000d005a
 #define HID_DG_TOOLSERIALNUMBER 0x000d005b