[PATCH v2 1/5] Input: edt-ft5x06: work around first register access error

[Marco Felsch <m.felsch@pengutronix.de>]

From: Philipp Zabel <p.zabel@pengutronix.de>

The EP0700MLP1 returns bogus data on the first register read access
(reading the threshold parameter from register 0x00):

    edt_ft5x06 2-0038: crc error: 0xfc expected, got 0x40

It ignores writes until then. This patch adds a dummy read after which
the number of sensors and parameter read/writes work correctly.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
---
 drivers/input/touchscreen/edt-ft5x06.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/input/touchscreen/edt-ft5x06.c b/drivers/input/touchscreen/edt-ft5x06.c
index d61731c0037d..b87b1e074f62 100644
--- a/drivers/input/touchscreen/edt-ft5x06.c
+++ b/drivers/input/touchscreen/edt-ft5x06.c
@@ -1050,6 +1050,7 @@ static int edt_ft5x06_ts_probe(struct i2c_client *client,
 {
 	const struct edt_i2c_chip_data *chip_data;
 	struct edt_ft5x06_ts_data *tsdata;
+	u8 buf[2] = { 0xfc, 0x00 };
 	struct input_dev *input;
 	unsigned long irq_flags;
 	int error;
@@ -1140,6 +1141,12 @@ static int edt_ft5x06_ts_probe(struct i2c_client *client,
 		return error;
 	}
 
+	/*
+	 * Dummy read access. EP0700MLP1 returns bogus data on the first
+	 * register read access and ignores writes.
+	 */
+	edt_ft5x06_ts_readwrite(tsdata->client, 2, buf, 2, buf);
+
 	edt_ft5x06_ts_set_regs(tsdata);
 	edt_ft5x06_ts_get_defaults(&client->dev, tsdata);
 	edt_ft5x06_ts_get_parameters(tsdata);
-- 
2.20.1