platform/chrome: chromeos_laptop - Add elan trackpad option for C720

Add the elan trackpad to the Acer C720 (peppy) list, as it is an alternate
trackpad option. It may exist at i2c address 0x15.

Based on this change from the chromeos kernel :
https://chromium-review.googlesource.com/186253Signed-off-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Olof Johansson <olof@lixom.net>

drivers/platform/chrome/chromeos_laptop.c

@@ -34,6 +34,7 @@
 #define ATMEL_TS_I2C_ADDR	0x4a
 #define ATMEL_TS_I2C_BL_ADDR	0x26
 #define CYAPA_TP_I2C_ADDR	0x67
+#define ELAN_TP_I2C_ADDR	0x15
 #define ISL_ALS_I2C_ADDR	0x44
 #define TAOS_ALS_I2C_ADDR	0x29
 
@@ -73,7 +74,7 @@ struct i2c_peripheral {
 	int tries;
 };
 
-#define MAX_I2C_PERIPHERALS 3
+#define MAX_I2C_PERIPHERALS 4
 
 struct chromeos_laptop {
 	struct i2c_peripheral i2c_peripherals[MAX_I2C_PERIPHERALS];
@@ -86,6 +87,11 @@ static struct i2c_board_info cyapa_device = {
 	.flags		= I2C_CLIENT_WAKE,
 };
 
+static struct i2c_board_info elantech_device = {
+	I2C_BOARD_INFO("elan_i2c", ELAN_TP_I2C_ADDR),
+	.flags		= I2C_CLIENT_WAKE,
+};
+
 static struct i2c_board_info isl_als_device = {
 	I2C_BOARD_INFO("isl29018", ISL_ALS_I2C_ADDR),
 };
@@ -306,6 +312,16 @@ static int setup_atmel_224s_tp(enum i2c_adapter_type type)
 	return (!tp) ? -EAGAIN : 0;
 }
 
+static int setup_elantech_tp(enum i2c_adapter_type type)
+{
+	if (tp)
+		return 0;
+
+	/* add elantech touchpad */
+	tp = add_i2c_device("trackpad", type, &elantech_device);
+	return (!tp) ? -EAGAIN : 0;
+}
+
 static int setup_atmel_1664s_ts(enum i2c_adapter_type type)
 {
 	const unsigned short addr_list[] = { ATMEL_TS_I2C_BL_ADDR,
@@ -475,6 +491,8 @@ static struct chromeos_laptop acer_c720 = {
 		{ .add = setup_atmel_1664s_ts, I2C_ADAPTER_DESIGNWARE_1 },
 		/* Touchpad. */
 		{ .add = setup_cyapa_tp, I2C_ADAPTER_DESIGNWARE_0 },
+		/* Elan Touchpad option. */
+		{ .add = setup_elantech_tp, I2C_ADAPTER_DESIGNWARE_0 },
 		/* Light Sensor. */
 		{ .add = setup_isl29018_als, I2C_ADAPTER_DESIGNWARE_1 },
 	},