iio: st_accel: support 8bit channel data

Some sensors like the LIS331DL only support 8bit data by a single
register per axis. These utilize the MSB byte. Make it possible
to register these apropriately.

A oneliner change is needed in the ST sensors core to handle 8bit
reads as this is the first supported 8bit sensor.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Denis Ciocca <denis.ciocca@st.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/accel/st_accel_core.c

@@ -153,6 +153,22 @@
 #define ST_ACCEL_4_IG1_EN_MASK			0x08
 #define ST_ACCEL_4_MULTIREAD_BIT		true
 
+static const struct iio_chan_spec st_accel_8bit_channels[] = {
+	ST_SENSORS_LSM_CHANNELS(IIO_ACCEL,
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+			ST_SENSORS_SCAN_X, 1, IIO_MOD_X, 's', IIO_LE, 8, 8,
+			ST_ACCEL_DEFAULT_OUT_X_L_ADDR+1),
+	ST_SENSORS_LSM_CHANNELS(IIO_ACCEL,
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+			ST_SENSORS_SCAN_Y, 1, IIO_MOD_Y, 's', IIO_LE, 8, 8,
+			ST_ACCEL_DEFAULT_OUT_Y_L_ADDR+1),
+	ST_SENSORS_LSM_CHANNELS(IIO_ACCEL,
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+			ST_SENSORS_SCAN_Z, 1, IIO_MOD_Z, 's', IIO_LE, 8, 8,
+			ST_ACCEL_DEFAULT_OUT_Z_L_ADDR+1),
+	IIO_CHAN_SOFT_TIMESTAMP(3)
+};
+
 static const struct iio_chan_spec st_accel_12bit_channels[] = {
 	ST_SENSORS_LSM_CHANNELS(IIO_ACCEL,
 			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),

drivers/iio/common/st_sensors/st_sensors_core.c

@@ -433,7 +433,9 @@ static int st_sensors_read_axis_data(struct iio_dev *indio_dev,
 	if (err < 0)
 		goto st_sensors_free_memory;
 
-	if (byte_for_channel == 2)
+	if (byte_for_channel == 1)
+		*data = (s8)*outdata;
+	else if (byte_for_channel == 2)
 		*data = (s16)get_unaligned_le16(outdata);
 	else if (byte_for_channel == 3)
 		*data = (s32)st_sensors_get_unaligned_le24(outdata);