Input: st1232 - wait until device is ready before reading resolution

According to the st1232 datasheet, the host has to wait for the device
to change into Normal state before accessing registers other than the
Status Register.

If the reset GPIO is wired, the device is powered on during driver
probe, just before reading the resolution.  However, the latter may
happen before the device is ready, leading to a probe failure:

    st1232-ts 1-0055: Failed to read resolution: -6

Fix this by waiting until the device is ready, by trying to read the
Status Register until it indicates so, or until timeout.

On Armadillo 800 EVA, typically the first read fails with an I2C
transfer error, while the second read indicates the device is ready.

Fixes: 3a54a21541 ("Input: st1232 - add support resolution reading")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201229162601.2154566-4-geert+renesas@glider.be
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/st1232.c

@@ -26,6 +26,20 @@
 #define ST1232_TS_NAME	"st1232-ts"
 #define ST1633_TS_NAME	"st1633-ts"
 
+#define REG_STATUS		0x01	/* Device Status | Error Code */
+
+#define STATUS_NORMAL		0x00
+#define STATUS_INIT		0x01
+#define STATUS_ERROR		0x02
+#define STATUS_AUTO_TUNING	0x03
+#define STATUS_IDLE		0x04
+#define STATUS_POWER_DOWN	0x05
+
+#define ERROR_NONE		0x00
+#define ERROR_INVALID_ADDRESS	0x10
+#define ERROR_INVALID_VALUE	0x20
+#define ERROR_INVALID_PLATFORM	0x30
+
 #define REG_XY_RESOLUTION	0x04
 #define REG_XY_COORDINATES	0x12
 #define ST_TS_MAX_FINGERS	10
@@ -73,6 +87,22 @@ static int st1232_ts_read_data(struct st1232_ts_data *ts, u8 reg,
 	return 0;
 }
 
+static int st1232_ts_wait_ready(struct st1232_ts_data *ts)
+{
+	unsigned int retries;
+	int error;
+
+	for (retries = 10; retries; retries--) {
+		error = st1232_ts_read_data(ts, REG_STATUS, 1);
+		if (!error && ts->read_buf[0] == (STATUS_NORMAL | ERROR_NONE))
+			return 0;
+
+		usleep_range(1000, 2000);
+	}
+
+	return -ENXIO;
+}
+
 static int st1232_ts_read_resolution(struct st1232_ts_data *ts, u16 *max_x,
 				     u16 *max_y)
 {
@@ -252,6 +282,11 @@ static int st1232_ts_probe(struct i2c_client *client,
 	input_dev->name = "st1232-touchscreen";
 	input_dev->id.bustype = BUS_I2C;
 
+	/* Wait until device is ready */
+	error = st1232_ts_wait_ready(ts);
+	if (error)
+		return error;
+
 	/* Read resolution from the chip */
 	error = st1232_ts_read_resolution(ts, &max_x, &max_y);
 	if (error) {