This patch adds optional regulators, which can be used to power
up touchscreen. After enabling regulators, we need to wait 150msec.
This value is taken from official driver.

It was tested on Samsung Galaxy i9000 (based on Samsung S5PV210 SOC).

Signed-off-by: Paweł Chmiel <redacted>
---
Changes from v3:
  - Fix checkpatch issues
  - Drop sentence punctuation from subject of one of patches

Changes from v2:
  - Move code enabling regulators into separate method,
    to make code more readable.

Changes from v1:
  - Enable regulators only if reset_gpio is present.
  - Switch from devm_regulator_get_optional to devm_regulator_get
---
 drivers/input/touchscreen/atmel_mxt_ts.c | 65 +++++++++++++++++++++---
 1 file changed, 59 insertions(+), 6 deletions(-)

diff --git a/drivers/input/touchscreen/atmel_mxt_ts.c b/drivers/input/touchscreen/atmel_mxt_ts.c
index d3aacd534e9c..1dc8ad0da5af 100644
--- a/drivers/input/touchscreen/atmel_mxt_ts.c
+++ b/drivers/input/touchscreen/atmel_mxt_ts.c

@@ -27,6 +27,7 @@
 #include <linux/interrupt.h>
 #include <linux/of.h>
 #include <linux/property.h>
+#include <linux/regulator/consumer.h>
 #include <linux/slab.h>
 #include <linux/gpio/consumer.h>
 #include <asm/unaligned.h>

@@ -194,10 +195,10 @@ enum t100_type {
 
 /* Delay times */
 #define MXT_BACKUP_TIME		50	/* msec */
-#define MXT_RESET_GPIO_TIME	20	/* msec */
 #define MXT_RESET_INVALID_CHG	100	/* msec */
 #define MXT_RESET_TIME		200	/* msec */
 #define MXT_RESET_TIMEOUT	3000	/* msec */
+#define MXT_REGULATOR_DELAY	150	/* msec */
 #define MXT_CRC_TIMEOUT		1000	/* msec */
 #define MXT_FW_RESET_TIME	3000	/* msec */
 #define MXT_FW_CHG_TIMEOUT	300	/* msec */

@@ -323,6 +324,8 @@ struct mxt_data {
 	struct t7_config t7_cfg;
 	struct mxt_dbg dbg;
 	struct gpio_desc *reset_gpio;
+	struct regulator *vdd_reg;
+	struct regulator *avdd_reg;
 
 	/* Cached parameters from object table */
 	u16 T5_address;

@@ -3038,6 +3041,38 @@ static const struct dmi_system_id chromebook_T9_suspend_dmi[] = {
 	{ }
 };
 
+static int mxt_regulator_enable(struct mxt_data *data)
+{
+	int error;
+
+	if (data->reset_gpio) {
+		error = regulator_enable(data->vdd_reg);
+		if (error) {
+			dev_err(&data->client->dev,
+				"Failed to enable vdd regulator: %d\n", error);
+			return error;
+		}
+
+		error = regulator_enable(data->avdd_reg);
+		if (error) {
+			dev_err(&data->client->dev,
+				"Failed to enable avdd regulator: %d\n", error);