iio: accel: adxl345: Add spi-3wire option

Add a setup function implementation to the spi module to enable spi-3wire
when specified in the device-tree. If spi-3wire is not specified in the
device-tree, NULL is returned as bus pre-initialization. This behavior
is identical to the i2c initialization, hence the default initialization.
Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Link: https://lore.kernel.org/r/20240401194906.56810-9-l.rubusch@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/accel/adxl345.h

@@ -31,6 +31,7 @@
 #define ADXL345_DATA_FORMAT_RANGE	GENMASK(1, 0)	/* Set the g range */
 #define ADXL345_DATA_FORMAT_JUSTIFY	BIT(2)	/* Left-justified (MSB) mode */
 #define ADXL345_DATA_FORMAT_FULL_RES	BIT(3)	/* Up to 13-bits resolution */
+#define ADXL345_DATA_FORMAT_SPI_3WIRE	BIT(6)	/* 3-wire SPI mode */
 #define ADXL345_DATA_FORMAT_SELF_TEST	BIT(7)	/* Enable a self test */
 
 #define ADXL345_DATA_FORMAT_2G		0

drivers/iio/accel/adxl345_spi.c

@@ -20,6 +20,11 @@ static const struct regmap_config adxl345_spi_regmap_config = {
 	.read_flag_mask = BIT(7) | BIT(6),
 };
 
+static int adxl345_spi_setup(struct device *dev, struct regmap *regmap)
+{
+	return regmap_write(regmap, ADXL345_REG_DATA_FORMAT, ADXL345_DATA_FORMAT_SPI_3WIRE);
+}
+
 static int adxl345_spi_probe(struct spi_device *spi)
 {
 	struct regmap *regmap;
@@ -33,7 +38,10 @@ static int adxl345_spi_probe(struct spi_device *spi)
 	if (IS_ERR(regmap))
 		return dev_err_probe(&spi->dev, PTR_ERR(regmap), "Error initializing regmap\n");
 
-	return adxl345_core_probe(&spi->dev, regmap, NULL);
+	if (spi->mode & SPI_3WIRE)
+		return adxl345_core_probe(&spi->dev, regmap, adxl345_spi_setup);
+	else
+		return adxl345_core_probe(&spi->dev, regmap, NULL);
 }
 
 static const struct adxl345_chip_info adxl345_spi_info = {