Input: elantech - packet checking for v2 hardware

For v2 hardware, there is no real parity check, but we can still check
some constant bits for data integrity.

Also rename elantech_check_parity_v1 to elantech_packet_check_v1 to make
these packet checking function names consistent.

Signed-off-by: JJ Ding <jj_ding@emc.com.tw>
Acked-by: Daniel Kurtz <djkurtz@chromium.org>
Acked-by: Éric Piel <eric.piel@tremplin-utc.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

1 files changed, 34 insertions, 5 deletions

diff --git a/drivers/input/mouse/elantech.c b/drivers/input/mouse/elantech.c
index 296b6a6250fd..f2e3a2be041c 100644
--- a/drivers/input/mouse/elantech.c
+++ b/drivers/input/mouse/elantech.c
@@ -350,7 +350,7 @@ static void elantech_report_absolute_v2(struct psmouse *psmouse)
         input_sync(dev);
 }
 
-static int elantech_check_parity_v1(struct psmouse *psmouse)
+static int elantech_packet_check_v1(struct psmouse *psmouse)
 {
         struct elantech_data *etd = psmouse->private;
         unsigned char *packet = psmouse->packet;
@@ -374,6 +374,34 @@ static int elantech_check_parity_v1(struct psmouse *psmouse)
                etd->parity[packet[3]] == p3;
 }
 
+static int elantech_packet_check_v2(struct psmouse *psmouse)
+{
+        struct elantech_data *etd = psmouse->private;
+        unsigned char *packet = psmouse->packet;
+
+        /*
+         * V2 hardware has two flavors. Older ones that do not report pressure,
+         * and newer ones that reports pressure and width. With newer ones, all
+         * packets (1, 2, 3 finger touch) have the same constant bits. With
+         * older ones, 1/3 finger touch packets and 2 finger touch packets
+         * have different constant bits.
+         * With all three cases, if the constant bits are not exactly what I
+         * expected, I consider them invalid.
+         */
+        if (etd->reports_pressure)
+                return (packet[0] & 0x0c) == 0x04 &&
+                       (packet[3] & 0x0f) == 0x02;
+
+        if ((packet[0] & 0xc0) == 0x80)
+                return (packet[0] & 0x0c) == 0x0c &&
+                       (packet[3] & 0x0e) == 0x08;
+
+        return (packet[0] & 0x3c) == 0x3c &&
+               (packet[1] & 0xf0) == 0x00 &&
+               (packet[3] & 0x3e) == 0x38 &&
+               (packet[4] & 0xf0) == 0x00;
+}
+
 /*
  * Process byte stream from mouse and handle complete packets
  */
@@ -389,14 +417,16 @@ static psmouse_ret_t elantech_process_byte(struct psmouse *psmouse)
 
         switch (etd->hw_version) {
         case 1:
-                if (etd->paritycheck && !elantech_check_parity_v1(psmouse))
+                if (etd->paritycheck && !elantech_packet_check_v1(psmouse))
                         return PSMOUSE_BAD_DATA;
 
                 elantech_report_absolute_v1(psmouse);
                 break;
 
         case 2:
-                /* We don't know how to check parity in protocol v2 */
+                if (etd->paritycheck && !elantech_packet_check_v2(psmouse))
+                        return PSMOUSE_BAD_DATA;
+
                 elantech_report_absolute_v2(psmouse);
                 break;
         }
@@ -795,8 +825,7 @@ int elantech_init(struct psmouse *psmouse)
                 etd->hw_version = 2;
                 /* For now show extra debug information */
                 etd->debug = 1;
-                /* Don't know how to do parity checking for version 2 */
-                etd->paritycheck = 0;
+                etd->paritycheck = 1;
 
                 if (etd->fw_version >= 0x020800)
                         etd->reports_pressure = true;