Re: [PATCH 3/6] 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.

Signed-off-by: JJ Ding <redacted>
---
 drivers/input/mouse/elantech.c |   26 +++++++++++++++++++++++---
 1 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/drivers/input/mouse/elantech.c b/drivers/input/mouse/elantech.c
index cf41f23..032181c 100644
--- a/drivers/input/mouse/elantech.c
+++ b/drivers/input/mouse/elantech.c

@@ -376,6 +376,25 @@ static int elantech_check_parity_v1(struct psmouse *psmouse)
              etd->parity[packet[3]] == p3;
 }

+static int packet_simple_check_v2(struct psmouse *psmouse)
+{
+       struct elantech_data *etd = psmouse->private;
+       unsigned char *packet = psmouse->packet;
+
+       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
 */

@@ -398,7 +417,9 @@ static psmouse_ret_t elantech_process_byte(struct psmouse *psmouse)
               break;

       case 2:
-               /* We don't know how to check parity in protocol v2 */
+               if (etd->paritycheck && !packet_simple_check_v2(psmouse))
+                       return PSMOUSE_BAD_DATA;
+
               elantech_report_absolute_v2(psmouse);
               break;
       }

@@ -799,8 +820,7 @@ 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;