iio: st_sensors: simplify buffer address handling

BugLink: https://bugs.launchpad.net/bugs/1676356

The driver goes to some length to dynamically allocate an array
to hold the channel addresses. However no ST sensor has more than
three channels (x, y, z at most). Instead of kmalloc():ing and
kfree():in the address array, just use a fixed array of three
elements.

Cc: Giuseppe Barba <giuseppe.barba@st.com>
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>
(cherry picked from commit e6e45420)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/iio/common/st_sensors/st_sensors_buffer.c

@@ -24,7 +24,7 @@
 
 int st_sensors_get_buffer_element(struct iio_dev *indio_dev, u8 *buf)
 {
-	u8 *addr;
+	u8 addr[3]; /* no ST sensor has more than 3 channels */
 	int i, n = 0, len;
 	struct st_sensor_data *sdata = iio_priv(indio_dev);
 	unsigned int num_data_channels = sdata->num_data_channels;
@@ -32,12 +32,6 @@ int st_sensors_get_buffer_element(struct iio_dev *indio_dev, u8 *buf)
 		DIV_ROUND_UP(indio_dev->channels[0].scan_type.realbits +
 				indio_dev->channels[0].scan_type.shift, 8);
 
-	addr = kmalloc(num_data_channels, GFP_KERNEL);
-	if (!addr) {
-		len = -ENOMEM;
-		goto st_sensors_get_buffer_element_error;
-	}
-
 	for (i = 0; i < num_data_channels; i++) {
 		if (test_bit(i, indio_dev->active_scan_mask)) {
 			addr[n] = indio_dev->channels[i].address;
@@ -58,10 +52,8 @@ int st_sensors_get_buffer_element(struct iio_dev *indio_dev, u8 *buf)
 			u8 *rx_array;
 			rx_array = kmalloc(byte_for_channel * num_data_channels,
 					   GFP_KERNEL);
-			if (!rx_array) {
-				len = -ENOMEM;
-				goto st_sensors_free_memory;
-			}
+			if (!rx_array)
+				return -ENOMEM;
 
 			len = sdata->tf->read_multiple_byte(&sdata->tb,
 				sdata->dev, addr[0],
@@ -69,7 +61,7 @@ int st_sensors_get_buffer_element(struct iio_dev *indio_dev, u8 *buf)
 				rx_array, sdata->multiread_bit);
 			if (len < 0) {
 				kfree(rx_array);
-				goto st_sensors_free_memory;
+				return len;
 			}
 
 			for (i = 0; i < n * byte_for_channel; i++) {
@@ -88,17 +80,11 @@ int st_sensors_get_buffer_element(struct iio_dev *indio_dev, u8 *buf)
 			buf, sdata->multiread_bit);
 		break;
 	default:
-		len = -EINVAL;
-		goto st_sensors_free_memory;
-	}
-	if (len != byte_for_channel * n) {
-		len = -EIO;
-		goto st_sensors_free_memory;
+		return -EINVAL;
 	}
+	if (len != byte_for_channel * n)
+		return -EIO;
 
-st_sensors_free_memory:
-	kfree(addr);
-st_sensors_get_buffer_element_error:
 	return len;
 }
 EXPORT_SYMBOL(st_sensors_get_buffer_element);