Input: synaptics - process finger (<=3) transitions

Synaptics image sensor touchpads track 5 fingers, but only report 2.
This patch attempts to deal with some idiosyncrasies of these touchpads:

 * When there are 3 or more fingers, only two are reported.
 * The touchpad tracks the 5 fingers in slot[0] through slot[4].
 * It always reports the lowest and highest valid slots in SGM and AGM
   packets, respectively.
 * The number of fingers is only reported in the SGM packet.  However,
   the number of fingers can change either before or after an AGM
   packet.
 * Thus, if an SGM reports a different number of fingers than the last
   SGM, it is impossible to tell whether the intervening AGM corresponds
   to the old number of fingers or the new number of fingers.
 * For example, when going from 2->3 fingers, it is not possible to tell
   whether tell AGM contains slot[1] (old 2nd finger) or slot[2] (new
   3rd finger).
 * When fingers are added one at at time, from 1->2->3, it is possible to
   track which slots are contained in the SGM and AGM packets:
     1 finger:  SGM = slot[0], no AGM
     2 fingers: SGM = slot[0], AGM = slot[1]
     3 fingers: SGM = slot[0], AGM = slot[2]
 * It is also possible to track which slot is contained in the SGM when 1
   of 2 fingers is removed.  This is because the touchpad sends a special
   (0,0,0) AGM packet whenever all fingers are removed except slot[0]:
     Last AGM == (0,0,0): SGM contains slot[1]
     Else: SGM contains slot[0]
 * However, once there are 3 fingers, if exactly 1 finger is removed, it
   is impossible to tell which 2 slots are contained in SGM and AGM.
   The (SGM,AGM) could be (0,1), (0,2), or (1,2). There is no way to know.
 * Similarly, if two fingers are simultaneously removed (3->1), then it
   is only possible to know if SGM still contains slot[0].
 * Since it is not possible to reliably track which slot is being
   reported, we invalidate the tracking_id every time the number of
   fingers changes until this ambiguity is resolved when:
     a) All fingers are removed.
     b) 4 or 5 fingers are touched, generates an AGM-CONTACT packet.
     c) All fingers are removed except slot[0].  In this special case, the
        ambiguity is resolved since by the (0,0,0) AGM packet.

Behavior of the driver:

When 2 or more fingers are present on the touchpad, the kernel reports
up to two MT-B slots containing the position data for two of the fingers
reported by the touchpad.  If the identity of a finger cannot be tracked
when the number-of-fingers changes, the corresponding MT-B slot will be
invalidated (track_id set to -1), and a new track_id will be assigned in
a subsequent input event report.

The driver always reports the total number of fingers using one of the
EV_KEY/BTN_TOOL_*TAP events. This could differ from the number of valid
MT-B slots for two reasons:
 a) There are more than 2 fingers on the pad.
 b) During ambiguous number-of-fingers transitions, the correct track_id
    for one or both of the slots cannot be determined, so the slots are
    invalidated.

Thus, this is a hybrid singletouch/MT-B scheme. Userspace can detect
this behavior by noting that the driver supports more EV_KEY/BTN_TOOL_*TAP
events than its maximum EV_ABS/ABS_MT_SLOT.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Acked-by: Chase Douglas <chase.douglas@canonical.com>
Acked-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

2 files changed, 278 insertions, 16 deletions

diff --git a/drivers/input/mouse/synaptics.c b/drivers/input/mouse/synaptics.c
index a7af8565e2de..aec9cf7124f8 100644
--- a/drivers/input/mouse/synaptics.c
+++ b/drivers/input/mouse/synaptics.c
@@ -453,6 +453,9 @@ static void synaptics_parse_agm(const unsigned char buf[],
         default:
                 break;
         }
+
+        /* Record that at least one AGM has been received since last SGM */
+        priv->agm_pending = true;
 }
 
 static int synaptics_parse_hw_state(const unsigned char buf[],
@@ -606,26 +609,53 @@ static void synaptics_report_slot(struct input_dev *dev, int slot,
 }
 
 static void synaptics_report_mt_data(struct psmouse *psmouse,
-                                     int count,
+                                     struct synaptics_mt_state *mt_state,
                                      const struct synaptics_hw_state *sgm)
 {
         struct input_dev *dev = psmouse->dev;
         struct synaptics_data *priv = psmouse->private;
         struct synaptics_hw_state *agm = &priv->agm;
+        struct synaptics_mt_state *old = &priv->mt_state;
 
-        switch (count) {
+        switch (mt_state->count) {
         case 0:
                 synaptics_report_slot(dev, 0, NULL);
                 synaptics_report_slot(dev, 1, NULL);
                 break;
         case 1:
-                synaptics_report_slot(dev, 0, sgm);
-                synaptics_report_slot(dev, 1, NULL);
+                if (mt_state->sgm == -1) {
+                        synaptics_report_slot(dev, 0, NULL);
+                        synaptics_report_slot(dev, 1, NULL);
+                } else if (mt_state->sgm == 0) {
+                        synaptics_report_slot(dev, 0, sgm);
+                        synaptics_report_slot(dev, 1, NULL);
+                } else {
+                        synaptics_report_slot(dev, 0, NULL);
+                        synaptics_report_slot(dev, 1, sgm);
+                }
                 break;
-        case 2:
-        case 3: /* Fall-through case */
-                synaptics_report_slot(dev, 0, sgm);
-                synaptics_report_slot(dev, 1, agm);
+        default:
+                /*
+                 * If the finger slot contained in SGM is valid, and either
+                 * hasn't changed, or is new, then report SGM in MTB slot 0.
+                 * Otherwise, empty MTB slot 0.
+                 */
+                if (mt_state->sgm != -1 &&
+                    (mt_state->sgm == old->sgm || old->sgm == -1))
+                        synaptics_report_slot(dev, 0, sgm);
+                else
+                        synaptics_report_slot(dev, 0, NULL);
+
+                /*
+                 * If the finger slot contained in AGM is valid, and either
+                 * hasn't changed, or is new, then report AGM in MTB slot 1.
+                 * Otherwise, empty MTB slot 1.
+                 */
+                if (mt_state->agm != -1 &&
+                    (mt_state->agm == old->agm || old->agm == -1))
+                        synaptics_report_slot(dev, 1, agm);
+                else
+                        synaptics_report_slot(dev, 1, NULL);
                 break;
         }
 
@@ -633,29 +663,257 @@ static void synaptics_report_mt_data(struct psmouse *psmouse,
         input_mt_report_pointer_emulation(dev, false);
 
         /* Send the number of fingers reported by touchpad itself. */
-        input_mt_report_finger_count(dev, count);
+        input_mt_report_finger_count(dev, mt_state->count);
 
         synaptics_report_buttons(psmouse, sgm);
 
         input_sync(dev);
 }
 
+/* Handle case where mt_state->count = 0 */
+static void synaptics_image_sensor_0f(struct synaptics_data *priv,
+                                      struct synaptics_mt_state *mt_state)
+{
+        synaptics_mt_state_set(mt_state, 0, -1, -1);
+        priv->mt_state_lost = false;
+}
+
+/* Handle case where mt_state->count = 1 */
+static void synaptics_image_sensor_1f(struct synaptics_data *priv,
+                                      struct synaptics_mt_state *mt_state)
+{
+        struct synaptics_hw_state *agm = &priv->agm;
+        struct synaptics_mt_state *old = &priv->mt_state;
+
+        /*
+         * If the last AGM was (0,0,0), and there is only one finger left,
+         * then we absolutely know that SGM contains slot 0, and all other
+         * fingers have been removed.
+         */
+        if (priv->agm_pending && agm->z == 0) {
+                synaptics_mt_state_set(mt_state, 1, 0, -1);
+                priv->mt_state_lost = false;
+                return;
+        }
+
+        switch (old->count) {
+        case 0:
+                synaptics_mt_state_set(mt_state, 1, 0, -1);
+                break;
+        case 1:
+                /*
+                 * If mt_state_lost, then the previous transition was 3->1,
+                 * and SGM now contains either slot 0 or 1, but we don't know
+                 * which.  So, we just assume that the SGM now contains slot 1.
+                 *
+                 * If pending AGM and either:
+                 *   (a) the previous SGM slot contains slot 0, or
+                 *   (b) there was no SGM slot
+                 * then, the SGM now contains slot 1
+                 *
+                 * Case (a) happens with very rapid "drum roll" gestures, where
+                 * slot 0 finger is lifted and a new slot 1 finger touches
+                 * within one reporting interval.
+                 *
+                 * Case (b) happens if initially two or more fingers tap
+                 * briefly, and all but one lift before the end of the first
+                 * reporting interval.
+                 *
+                 * (In both these cases, slot 0 will becomes empty, so SGM
+                 * contains slot 1 with the new finger)
+                 *
+                 * Else, if there was no previous SGM, it now contains slot 0.
+                 *
+                 * Otherwise, SGM still contains the same slot.
+                 */
+                if (priv->mt_state_lost ||
+                    (priv->agm_pending && old->sgm <= 0))
+                        synaptics_mt_state_set(mt_state, 1, 1, -1);
+                else if (old->sgm == -1)
+                        synaptics_mt_state_set(mt_state, 1, 0, -1);
+                break;
+        case 2:
+                /*
+                 * If mt_state_lost, we don't know which finger SGM contains.
+                 *
+                 * So, report 1 finger, but with both slots empty.
+                 * We will use slot 1 on subsequent 1->1
+                 */
+                if (priv->mt_state_lost) {
+                        synaptics_mt_state_set(mt_state, 1, -1, -1);
+                        break;
+                }
+                /*
+                 * Since the last AGM was NOT (0,0,0), it was the finger in
+                 * slot 0 that has been removed.
+                 * So, SGM now contains previous AGM's slot, and AGM is now
+                 * empty.
+                 */
+                synaptics_mt_state_set(mt_state, 1, old->agm, -1);
+                break;
+        case 3:
+                /*
+                 * Since last AGM was not (0,0,0), we don't know which finger
+                 * is left.
+                 *
+                 * So, report 1 finger, but with both slots empty.
+                 * We will use slot 1 on subsequent 1->1
+                 */
+                synaptics_mt_state_set(mt_state, 1, -1, -1);
+                priv->mt_state_lost = true;
+                break;
+        }
+}
+
+/* Handle case where mt_state->count = 2 */
+static void synaptics_image_sensor_2f(struct synaptics_data *priv,
+                                      struct synaptics_mt_state *mt_state)
+{
+        struct synaptics_mt_state *old = &priv->mt_state;
+
+        switch (old->count) {
+        case 0:
+                synaptics_mt_state_set(mt_state, 2, 0, 1);
+                break;
+        case 1:
+                /*
+                 * If previous SGM contained slot 1 or higher, SGM now contains
+                 * slot 0 (the newly touching finger) and AGM contains SGM's
+                 * previous slot.
+                 *
+                 * Otherwise, SGM still contains slot 0 and AGM now contains
+                 * slot 1.
+                 */
+                if (old->sgm >= 1)
+                        synaptics_mt_state_set(mt_state, 2, 0, old->sgm);
+                else
+                        synaptics_mt_state_set(mt_state, 2, 0, 1);
+                break;
+        case 2:
+                /*
+                 * If mt_state_lost, SGM now contains either finger 1 or 2, but
+                 * we don't know which.
+                 * So, we just assume that the SGM contains slot 0 and AGM 1.
+                 */
+                if (priv->mt_state_lost)
+                        synaptics_mt_state_set(mt_state, 2, 0, 1);
+                /*
+                 * Otherwise, use the same mt_state, since it either hasn't
+                 * changed, or was updated by a recently received AGM-CONTACT
+                 * packet.
+                 */
+                break;
+        case 3:
+                /*
+                 * 3->2 transitions have two unsolvable problems:
+                 *  1) no indication is given which finger was removed
+                 *  2) no way to tell if agm packet was for finger 3
+                 *     before 3->2, or finger 2 after 3->2.
+                 *
+                 * So, report 2 fingers, but empty all slots.
+                 * We will guess slots [0,1] on subsequent 2->2.
+                 */
+                synaptics_mt_state_set(mt_state, 2, -1, -1);
+                priv->mt_state_lost = true;
+                break;
+        }
+}
+
+/* Handle case where mt_state->count = 3 */
+static void synaptics_image_sensor_3f(struct synaptics_data *priv,
+                                      struct synaptics_mt_state *mt_state)
+{
+        struct synaptics_mt_state *old = &priv->mt_state;
+
+        switch (old->count) {
+        case 0:
+                synaptics_mt_state_set(mt_state, 3, 0, 2);
+                break;
+        case 1:
+                /*
+                 * If previous SGM contained slot 2 or higher, SGM now contains
+                 * slot 0 (one of the newly touching fingers) and AGM contains
+                 * SGM's previous slot.
+                 *
+                 * Otherwise, SGM now contains slot 0 and AGM contains slot 2.
+                 */
+                if (old->sgm >= 2)
+                        synaptics_mt_state_set(mt_state, 3, 0, old->sgm);
+                else
+                        synaptics_mt_state_set(mt_state, 3, 0, 2);
+                break;
+        case 2:
+                /*
+                 * After some 3->1 and all 3->2 transitions, we lose track
+                 * of which slot is reported by SGM and AGM.
+                 *
+                 * For 2->3 in this state, report 3 fingers, but empty all
+                 * slots, and we will guess (0,2) on a subsequent 0->3.
+                 *
+                 * To userspace, the resulting transition will look like:
+                 *    2:[0,1] -> 3:[-1,-1] -> 3:[0,2]
+                 */
+                if (priv->mt_state_lost) {
+                        synaptics_mt_state_set(mt_state, 3, -1, -1);
+                        break;
+                }
+
+                /*
+                 * If the (SGM,AGM) really previously contained slots (0, 1),
+                 * then we cannot know what slot was just reported by the AGM,
+                 * because the 2->3 transition can occur either before or after
+                 * the AGM packet. Thus, this most recent AGM could contain
+                 * either the same old slot 1 or the new slot 2.
+                 * Subsequent AGMs will be reporting slot 2.
+                 *
+                 * To userspace, the resulting transition will look like:
+                 *    2:[0,1] -> 3:[0,-1] -> 3:[0,2]
+                 */
+                synaptics_mt_state_set(mt_state, 3, 0, -1);
+                break;
+        case 3:
+                /*
+                 * If, for whatever reason, the previous agm was invalid,
+                 * Assume SGM now contains slot 0, AGM now contains slot 2.
+                 */
+                if (old->agm <= 2)
+                        synaptics_mt_state_set(mt_state, 3, 0, 2);
+                /*
+                 * mt_state either hasn't changed, or was updated by a recently
+                 * received AGM-CONTACT packet.
+                 */
+                break;
+        }
+}
+
 static void synaptics_image_sensor_process(struct psmouse *psmouse,
                                            struct synaptics_hw_state *sgm)
 {
-        int count;
+        struct synaptics_data *priv = psmouse->private;
+        struct synaptics_hw_state *agm = &priv->agm;
+        struct synaptics_mt_state mt_state;
 
+        /* Initialize using current mt_state (as updated by last agm) */
+        mt_state = agm->mt_state;
+
+        /*
+         * Update mt_state using the new finger count and current mt_state.
+         */
         if (sgm->z == 0)
-                count = 0;
+                synaptics_image_sensor_0f(priv, &mt_state);
         else if (sgm->w >= 4)
-                count = 1;
+                synaptics_image_sensor_1f(priv, &mt_state);
         else if (sgm->w == 0)
-                count = 2;
-        else
-                count = 3;
+                synaptics_image_sensor_2f(priv, &mt_state);
+        else if (sgm->w == 1)
+                synaptics_image_sensor_3f(priv, &mt_state);
 
         /* Send resulting input events to user space */
-        synaptics_report_mt_data(psmouse, count, sgm);
+        synaptics_report_mt_data(psmouse, &mt_state, sgm);
+
+        /* Store updated mt_state */
+        priv->mt_state = agm->mt_state = mt_state;
+        priv->agm_pending = false;
 }
 
 /*
diff --git a/drivers/input/mouse/synaptics.h b/drivers/input/mouse/synaptics.h
index 20f57dfebed1..622aea8dd7e0 100644
--- a/drivers/input/mouse/synaptics.h
+++ b/drivers/input/mouse/synaptics.h
@@ -161,11 +161,15 @@ struct synaptics_data {
 
         struct serio *pt_port;                  /* Pass-through serio port */
 
+        struct synaptics_mt_state mt_state;     /* Current mt finger state */
+        bool mt_state_lost;                     /* mt_state may be incorrect */
+
         /*
          * Last received Advanced Gesture Mode (AGM) packet. An AGM packet
          * contains position data for a second contact, at half resolution.
          */
         struct synaptics_hw_state agm;
+        bool agm_pending;                       /* new AGM packet received */
 };
 
 void synaptics_module_init(void);