The Pixcir Tango controller has support for a one-time total calibration
(manual calibration) procedure. Its purpose is to measure the capacitance
offsets of the electrode system and to store these values into EEPROM.

During normal operation this calibration data is subtracted from the values
measured. This calibration should be necessary only once in the product
lifetime. It should be performed as part of the final adjustment after
the panel is mounted in the product.

Add support for the calibration with sysfs interface.

Signed-off-by: Michal Vokáč <michal.vokac@ysoft.com>
---
changes in v2:
 - Removed redundant lock from calibrate_store().

 drivers/input/touchscreen/pixcir_i2c_ts.c | 26 +++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/input/touchscreen/pixcir_i2c_ts.c b/drivers/input/touchscreen/pixcir_i2c_ts.c
index dad5786e82a4..e52ec8d8e392 100644
--- a/drivers/input/touchscreen/pixcir_i2c_ts.c
+++ b/drivers/input/touchscreen/pixcir_i2c_ts.c
@@ -24,6 +24,7 @@
  */
 #define PIXCIR_REG_POWER_MODE	51
 #define PIXCIR_REG_INT_MODE	52
+#define PIXCIR_REG_SPECOP	58
 
 /*
  * Power modes:
@@ -462,6 +463,30 @@ static int pixcir_i2c_ts_resume(struct device *dev)
 static DEFINE_SIMPLE_DEV_PM_OPS(pixcir_dev_pm_ops,
 				pixcir_i2c_ts_suspend, pixcir_i2c_ts_resume);
 
+static ssize_t calibrate_store(struct device *dev,
+			       struct device_attribute *attr,
+			       const char *buf, size_t count)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct pixcir_i2c_ts_data *ts = i2c_get_clientdata(client);
+	static const u8 cmd = 0x03;
+	int error;
+
+	error = i2c_smbus_write_byte_data(ts->client, PIXCIR_REG_SPECOP, cmd);
+	if (error)
+		dev_err(dev, "calibrate command failed: %d\n", error);
+
+	return error ?: count;
+}
+
+static DEVICE_ATTR_WO(calibrate);
+
+static struct attribute *pixcir_i2c_ts_attrs[] = {
+	&dev_attr_calibrate.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(pixcir_i2c_ts);
+
 static int pixcir_i2c_ts_probe(struct i2c_client *client)
 {
 	const struct i2c_device_id *id = i2c_client_get_device_id(client);
@@ -600,6 +625,7 @@ MODULE_DEVICE_TABLE(of, pixcir_of_match);
 static struct i2c_driver pixcir_i2c_ts_driver = {
 	.driver = {
 		.name	= "pixcir_ts",
+		.dev_groups = pixcir_i2c_ts_groups,
 		.pm	= pm_sleep_ptr(&pixcir_dev_pm_ops),
 		.of_match_table = of_match_ptr(pixcir_of_match),
 	},
-- 
2.43.0