Input: elo - fix checksum calculation

Fix 10-byte protocol checksum calculation and do not discard packet early
unless it is missing lead in byte.

Signed-off-by: Shaun Jackman <sjackman@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

1 files changed, 29 insertions, 26 deletions

diff --git a/drivers/input/touchscreen/elo.c b/drivers/input/touchscreen/elo.c
index b7ac016219d9..fe6e1a428674 100644
--- a/drivers/input/touchscreen/elo.c
+++ b/drivers/input/touchscreen/elo.c
@@ -34,7 +34,11 @@ MODULE_LICENSE("GPL");
  * Definitions & global arrays.
  */
 
-#define ELO_MAX_LENGTH  10
+#define ELO_MAX_LENGTH          10
+
+#define ELO10_LEAD_BYTE         'U'
+
+#define ELO10_TOUCH_PACKET      'T'
 
 /*
  * Per-touchscreen data.
@@ -50,44 +54,43 @@ struct elo {
         char phys[32];
 };
 
-static void elo_process_data_10(struct elo* elo, unsigned char data, struct pt_regs *regs)
+static void elo_process_data_10(struct elo *elo, unsigned char data, struct pt_regs *regs)
 {
         struct input_dev *dev = elo->dev;
 
-        elo->csum += elo->data[elo->idx] = data;
-
+        elo->data[elo->idx] = data;
         switch (elo->idx++) {
-
                 case 0:
-                        if (data != 'U') {
-                                elo->idx = 0;
-                                elo->csum = 0;
-                        }
-                        break;
-
-                case 1:
-                        if (data != 'T') {
+                        elo->csum = 0xaa;
+                        if (data != ELO10_LEAD_BYTE) {
+                                pr_debug("elo: unsynchronized data: 0x%02x\n", data);
                                 elo->idx = 0;
-                                elo->csum = 0;
                         }
                         break;
 
                 case 9:
-                        if (elo->csum) {
-                                input_regs(dev, regs);
-                                input_report_abs(dev, ABS_X, (elo->data[4] << 8) | elo->data[3]);
-                                input_report_abs(dev, ABS_Y, (elo->data[6] << 8) | elo->data[5]);
-                                input_report_abs(dev, ABS_PRESSURE, (elo->data[8] << 8) | elo->data[7]);
-                                input_report_key(dev, BTN_TOUCH, elo->data[8] || elo->data[7]);
-                                input_sync(dev);
-                        }
                         elo->idx = 0;
-                        elo->csum = 0;
+                        if (data != elo->csum) {
+                                pr_debug("elo: bad checksum: 0x%02x, expected 0x%02x\n",
+                                         data, elo->csum);
+                                break;
+                        }
+                        if (elo->data[1] != ELO10_TOUCH_PACKET) {
+                                pr_debug(elo: "unexpected packet: 0x%02x\n", elo->data[1]);
+                                break;
+                        }
+                        input_regs(dev, regs);
+                        input_report_abs(dev, ABS_X, (elo->data[4] << 8) | elo->data[3]);
+                        input_report_abs(dev, ABS_Y, (elo->data[6] << 8) | elo->data[5]);
+                        input_report_abs(dev, ABS_PRESSURE, (elo->data[8] << 8) | elo->data[7]);
+                        input_report_key(dev, BTN_TOUCH, elo->data[8] || elo->data[7]);
+                        input_sync(dev);
                         break;
         }
+        elo->csum += data;
 }
 
-static void elo_process_data_6(struct elo* elo, unsigned char data, struct pt_regs *regs)
+static void elo_process_data_6(struct elo *elo, unsigned char data, struct pt_regs *regs)
 {
         struct input_dev *dev = elo->dev;
 
@@ -135,7 +138,7 @@ static void elo_process_data_6(struct elo* elo, unsigned char data, struct pt_re
         }
 }
 
-static void elo_process_data_3(struct elo* elo, unsigned char data, struct pt_regs *regs)
+static void elo_process_data_3(struct elo *elo, unsigned char data, struct pt_regs *regs)
 {
         struct input_dev *dev = elo->dev;
 
@@ -161,7 +164,7 @@ static void elo_process_data_3(struct elo* elo, unsigned char data, struct pt_re
 static irqreturn_t elo_interrupt(struct serio *serio,
                 unsigned char data, unsigned int flags, struct pt_regs *regs)
 {
-        struct elo* elo = serio_get_drvdata(serio);
+        struct elo *elo = serio_get_drvdata(serio);
 
         switch(elo->id) {
                 case 0: