[PATCH v3 1/4] iio: adc: ad799x: make rx_buf static and DMA-safe

[Archit Anant]

Currently, rx_buf is dynamically allocated using kmalloc() every time
ad799x_update_scan_mode() is called. This can lead to memory leaks if
the scan mask is updated multiple times.

Drop the dynamic allocation and replace it with a static, buffer at the
end of the state structure using IIO_DECLARE_DMA_BUFFER_WITH_TS().
This eliminates the allocation overhead, prevents leaks, and removes
the need for manual kfree() on driver removal.

Suggested-by: David Lechner <dlechner@xxxxxxxxxxxx>
Signed-off-by: Archit Anant <architanant5@xxxxxxxxx>
---
 drivers/iio/adc/ad799x.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/iio/adc/ad799x.c b/drivers/iio/adc/ad799x.c
index 108bb22162ef..7775be874081 100644
--- a/drivers/iio/adc/ad799x.c
+++ b/drivers/iio/adc/ad799x.c
@@ -39,6 +39,7 @@
 #include <linux/iio/triggered_buffer.h>
 
 #define AD799X_CHANNEL_SHIFT			4
+#define AD799X_MAX_CHANNELS			8
 
 /*
  * AD7991, AD7995 and AD7999 defines
@@ -133,8 +134,8 @@ struct ad799x_state {
 	unsigned int			id;
 	u16				config;
 
-	u8				*rx_buf;
 	unsigned int			transfer_size;
+	IIO_DECLARE_DMA_BUFFER_WITH_TS(__be16, rx_buf, AD799X_MAX_CHANNELS);
 };
 
 static int ad799x_write_config(struct ad799x_state *st, u16 val)
@@ -217,11 +218,11 @@ static irqreturn_t ad799x_trigger_handler(int irq, void *p)
 	}
 
 	b_sent = i2c_smbus_read_i2c_block_data(st->client,
-			cmd, st->transfer_size, st->rx_buf);
+			cmd, st->transfer_size, (u8 *)st->rx_buf);
 	if (b_sent < 0)
 		goto out;
 
-	iio_push_to_buffers_with_timestamp(indio_dev, st->rx_buf,
+	iio_push_to_buffers_with_timestamp(indio_dev, &st->rx_buf,
 			iio_get_time_ns(indio_dev));
 out:
 	iio_trigger_notify_done(indio_dev->trig);
@@ -234,11 +235,6 @@ static int ad799x_update_scan_mode(struct iio_dev *indio_dev,
 {
 	struct ad799x_state *st = iio_priv(indio_dev);
 
-	kfree(st->rx_buf);
-	st->rx_buf = kmalloc(indio_dev->scan_bytes, GFP_KERNEL);
-	if (!st->rx_buf)
-		return -ENOMEM;
-
 	st->transfer_size = bitmap_weight(scan_mask,
 					  iio_get_masklength(indio_dev)) * 2;
 
@@ -895,7 +891,6 @@ static void ad799x_remove(struct i2c_client *client)
 	if (st->vref)
 		regulator_disable(st->vref);
 	regulator_disable(st->reg);
-	kfree(st->rx_buf);
 }
 
 static int ad799x_suspend(struct device *dev)
-- 
2.39.5