[PATCH v3] iio: st_sensors: drop temporary kmalloc buffer and reuse buffer_data

[PATCH v3] iio: st_sensors: drop temporary kmalloc buffer and reuse buffer_data

[Sanjay Chitroda]

From: Sanjay Chitroda <sanjayembeddedse@gmail.com>

Replace the per-call kmalloc() scratch buffer with the statically allocated
buffer_data[] field present in struct st_sensor_data. The existing buffer
is DMA-aligned and sufficiently sized for all channel widths, so using it
avoids unnecessary dynamic memory allocation on each read.

This simplifies the code, removes redundant allocation and cleanup.
No functional change intended.

Signed-off-by: Sanjay Chitroda <sanjayembeddedse@gmail.com>
---
Changes in v3:
- fix variable declartion placement to follow kernel coding style
- Link to v2 https://lore.kernel.org/all/20260311182050.3467471-1-sanjayembedded@gmail.com/
Changes in v2:
- split series to individual patch
- address review comment from David Lechner and reuse exising buffer instead of allocation
- Link to v1 https://lore.kernel.org/all/20260310200513.2162018-4-sanjayembedded@gmail.com/
---
 drivers/iio/common/st_sensors/st_sensors_core.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/common/st_sensors/st_sensors_core.c b/drivers/iio/common/st_sensors/st_sensors_core.c
index dac593be5695..dbc5e16fbde4 100644
--- a/drivers/iio/common/st_sensors/st_sensors_core.c
+++ b/drivers/iio/common/st_sensors/st_sensors_core.c
@@ -501,14 +501,12 @@ static int st_sensors_read_axis_data(struct iio_dev *indio_dev,
 
 	byte_for_channel = DIV_ROUND_UP(ch->scan_type.realbits +
 					ch->scan_type.shift, 8);
-	outdata = kmalloc(byte_for_channel, GFP_DMA | GFP_KERNEL);
-	if (!outdata)
-		return -ENOMEM;
+	outdata = sdata->buffer_data;
 
 	err = regmap_bulk_read(sdata->regmap, ch->address,
 			       outdata, byte_for_channel);
 	if (err < 0)
-		goto st_sensors_free_memory;
+		return err;
 
 	if (byte_for_channel == 1)
 		*data = (s8)*outdata;
@@ -517,10 +515,7 @@ static int st_sensors_read_axis_data(struct iio_dev *indio_dev,
 	else if (byte_for_channel == 3)
 		*data = (s32)sign_extend32(get_unaligned_le24(outdata), 23);
 
-st_sensors_free_memory:
-	kfree(outdata);
-
-	return err;
+	return 0;
 }
 
 int st_sensors_read_info_raw(struct iio_dev *indio_dev,
-- 
2.34.1

Re: [PATCH v3] iio: st_sensors: drop temporary kmalloc buffer and reuse buffer_data

[David Lechner]

On 3/12/26 1:34 AM, Sanjay Chitroda wrote:
> From: Sanjay Chitroda <sanjayembeddedse@gmail.com>
> 
> Replace the per-call kmalloc() scratch buffer with the statically allocated

"statically allocated" is a bit misleading. It is just an existing buffer
in the private driver data (dynamically allocated during probe). 

> buffer_data[] field present in struct st_sensor_data. The existing buffer
> is DMA-aligned and sufficiently sized for all channel widths, so using it
> avoids unnecessary dynamic memory allocation on each read.
> 
> This simplifies the code, removes redundant allocation and cleanup.
> No functional change intended.
> 
> Signed-off-by: Sanjay Chitroda <sanjayembeddedse@gmail.com>
> ---
Reviewed-by: David Lechner <dlechner@baylibre.com>