Input: ALPS - fix multi-touch decoding on SS4 plus touchpads

The fix for handling two-finger scroll (i4a646580f793 - "Input: ALPS -
fix two-finger scroll breakage in right side on ALPS touchpad")
introduced a minor "typo" that broke decoding of multi-touch events are
decoded on some ALPS touchpads.  For example, tapping with three-fingers
can no longer be used to emulate middle-mouse-button (the kernel doesn't
recognize this as the proper event, and doesn't report it correctly to
userspace).  This affects touchpads that use SS4 "plus" protocol
variant, like those found on Dell E7270 & E7470 laptops (tested on
E7270).

First, probably the code in alps_decode_ss4_v2() for case
SS4_PACKET_ID_MULTI used inconsistent indices to "f->mt[]". You can see
0 & 1 are used for the "if" part but 2 & 3 are used for the "else" part.

Second, in the previous patch, new macros were introduced to decode X
coordinates specific to the SS4 "plus" variant, but the macro to
define the maximum X value wasn't changed accordingly. The macros to
decode X values for "plus" variant are effectively shifted right by 1
bit, but the max wasn't shifted too. This causes the driver to
incorrectly handle "no data" cases, which also interfered with how
multi-touch was handled.

Fixes: 4a646580f793 ("Input: ALPS - fix two-finger scroll breakage...")
Signed-off-by: Nir Perry <nirperry@gmail.com>
Reviewed-by: Masaki Ota <masaki.ota@jp.alps.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

2 files changed, 19 insertions, 14 deletions

diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
index 579b899add26..dbe57da8c1a1 100644
--- a/drivers/input/mouse/alps.c
+++ b/drivers/input/mouse/alps.c
@@ -1250,29 +1250,32 @@ static int alps_decode_ss4_v2(struct alps_fields *f,
         case SS4_PACKET_ID_MULTI:
                 if (priv->flags & ALPS_BUTTONPAD) {
                         if (IS_SS4PLUS_DEV(priv->dev_id)) {
-                                f->mt[0].x = SS4_PLUS_BTL_MF_X_V2(p, 0);
-                                f->mt[1].x = SS4_PLUS_BTL_MF_X_V2(p, 1);
+                                f->mt[2].x = SS4_PLUS_BTL_MF_X_V2(p, 0);
+                                f->mt[3].x = SS4_PLUS_BTL_MF_X_V2(p, 1);
+                                no_data_x = SS4_PLUS_MFPACKET_NO_AX_BL;
                         } else {
                                 f->mt[2].x = SS4_BTL_MF_X_V2(p, 0);
                                 f->mt[3].x = SS4_BTL_MF_X_V2(p, 1);
+                                no_data_x = SS4_MFPACKET_NO_AX_BL;
                         }
+                        no_data_y = SS4_MFPACKET_NO_AY_BL;
 
                         f->mt[2].y = SS4_BTL_MF_Y_V2(p, 0);
                         f->mt[3].y = SS4_BTL_MF_Y_V2(p, 1);
-                        no_data_x = SS4_MFPACKET_NO_AX_BL;
-                        no_data_y = SS4_MFPACKET_NO_AY_BL;
                 } else {
                         if (IS_SS4PLUS_DEV(priv->dev_id)) {
-                                f->mt[0].x = SS4_PLUS_STD_MF_X_V2(p, 0);
-                                f->mt[1].x = SS4_PLUS_STD_MF_X_V2(p, 1);
+                                f->mt[2].x = SS4_PLUS_STD_MF_X_V2(p, 0);
+                                f->mt[3].x = SS4_PLUS_STD_MF_X_V2(p, 1);
+                                no_data_x = SS4_PLUS_MFPACKET_NO_AX;
                         } else {
-                                f->mt[0].x = SS4_STD_MF_X_V2(p, 0);
-                                f->mt[1].x = SS4_STD_MF_X_V2(p, 1);
+                                f->mt[2].x = SS4_STD_MF_X_V2(p, 0);
+                                f->mt[3].x = SS4_STD_MF_X_V2(p, 1);
+                                no_data_x = SS4_MFPACKET_NO_AX;
                         }
+                        no_data_y = SS4_MFPACKET_NO_AY;
+
                         f->mt[2].y = SS4_STD_MF_Y_V2(p, 0);
                         f->mt[3].y = SS4_STD_MF_Y_V2(p, 1);
-                        no_data_x = SS4_MFPACKET_NO_AX;
-                        no_data_y = SS4_MFPACKET_NO_AY;
                 }
 
                 f->first_mp = 0;
diff --git a/drivers/input/mouse/alps.h b/drivers/input/mouse/alps.h
index c80a7c76cb76..79b6d69d1486 100644
--- a/drivers/input/mouse/alps.h
+++ b/drivers/input/mouse/alps.h
@@ -141,10 +141,12 @@ enum SS4_PACKET_ID {
 #define SS4_TS_Z_V2(_b)         (s8)(_b[4] & 0x7F)
 
 
-#define SS4_MFPACKET_NO_AX      8160    /* X-Coordinate value */
-#define SS4_MFPACKET_NO_AY      4080    /* Y-Coordinate value */
-#define SS4_MFPACKET_NO_AX_BL   8176    /* Buttonless X-Coordinate value */
-#define SS4_MFPACKET_NO_AY_BL   4088    /* Buttonless Y-Coordinate value */
+#define SS4_MFPACKET_NO_AX              8160    /* X-Coordinate value */
+#define SS4_MFPACKET_NO_AY              4080    /* Y-Coordinate value */
+#define SS4_MFPACKET_NO_AX_BL           8176    /* Buttonless X-Coord value */
+#define SS4_MFPACKET_NO_AY_BL           4088    /* Buttonless Y-Coord value */
+#define SS4_PLUS_MFPACKET_NO_AX         4080    /* SS4 PLUS, X */
+#define SS4_PLUS_MFPACKET_NO_AX_BL      4088    /* Buttonless SS4 PLUS, X */
 
 /*
  * enum V7_PACKET_ID - defines the packet type for V7