[PATCH 1/2] iio: dac: ad5593r: Fix i2c read protocol requirements

[Nuno Sá <nuno.sa@xxxxxxxxxx>]

From: Michael Hennerich <michael.hennerich@xxxxxxxxxx>

For reliable operation across the full range of supported
interface rates, the AD5593R needs a STOP condition between
address write, and data read (like show in the datasheet Figure 40)
so in turn i2c_smbus_read_word_swapped cannot be used.

While at it, a simple helper was added to make the code simpler.

Fixes: 56ca9db862bf ("iio: dac: Add support for the AD5592R/AD5593R ADCs/DACs")
Signed-off-by: Michael Hennerich <michael.hennerich@xxxxxxxxxx>
Signed-off-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
---
 drivers/iio/dac/ad5593r.c | 44 +++++++++++++++++++++------------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/drivers/iio/dac/ad5593r.c b/drivers/iio/dac/ad5593r.c
index 34e1319a9712..43ee4efb250c 100644
--- a/drivers/iio/dac/ad5593r.c
+++ b/drivers/iio/dac/ad5593r.c
@@ -20,6 +20,24 @@
 #define AD5593R_MODE_GPIO_READBACK	(6 << 4)
 #define AD5593R_MODE_REG_READBACK	(7 << 4)
 
+static int ad5593r_read_word(struct i2c_client *i2c, u8 reg, u16 *value)
+{
+	int ret;
+	u8 buf[2];
+
+	ret = i2c_smbus_write_byte(i2c, reg);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_master_recv(i2c, buf, sizeof(buf));
+	if (ret < 0)
+		return ret;
+
+	*value = get_unaligned_be16(buf);
+
+	return 0;
+}
+
 static int ad5593r_write_dac(struct ad5592r_state *st, unsigned chan, u16 value)
 {
 	struct i2c_client *i2c = to_i2c_client(st->dev);
@@ -38,13 +56,7 @@ static int ad5593r_read_adc(struct ad5592r_state *st, unsigned chan, u16 *value)
 	if (val < 0)
 		return (int) val;
 
-	val = i2c_smbus_read_word_swapped(i2c, AD5593R_MODE_ADC_READBACK);
-	if (val < 0)
-		return (int) val;
-
-	*value = (u16) val;
-
-	return 0;
+	return ad5593r_read_word(i2c, AD5593R_MODE_ADC_READBACK, value);
 }
 
 static int ad5593r_reg_write(struct ad5592r_state *st, u8 reg, u16 value)
@@ -58,29 +70,21 @@ static int ad5593r_reg_write(struct ad5592r_state *st, u8 reg, u16 value)
 static int ad5593r_reg_read(struct ad5592r_state *st, u8 reg, u16 *value)
 {
 	struct i2c_client *i2c = to_i2c_client(st->dev);
-	s32 val;
-
-	val = i2c_smbus_read_word_swapped(i2c, AD5593R_MODE_REG_READBACK | reg);
-	if (val < 0)
-		return (int) val;
-
-	*value = (u16) val;
 
-	return 0;
+	return ad5593r_read_word(i2c, AD5593R_MODE_REG_READBACK | reg, value);
 }
 
 static int ad5593r_gpio_read(struct ad5592r_state *st, u8 *value)
 {
 	struct i2c_client *i2c = to_i2c_client(st->dev);
-	s32 val;
+	u16 val;
+	int ret;
 
-	val = i2c_smbus_read_word_swapped(i2c, AD5593R_MODE_GPIO_READBACK);
-	if (val < 0)
-		return (int) val;
+	ret = ad5593r_read_word(i2c, AD5593R_MODE_GPIO_READBACK, &val);
 
 	*value = (u8) val;
 
-	return 0;
+	return ret;
 }
 
 static const struct ad5592r_rw_ops ad5593r_rw_ops = {
-- 
2.37.3