[PATCH v7 9/9] iio: ssp_sensors: reuse embedded RX buffer for SPI transfers

Sanjay Chitroda
2026-04-26T09:18:00Z

From: Sanjay Chitroda <sanjayembeddedse@gmail.com>

Avoid allocating a temporary DMA buffer in the interrupt context when
handling hub-to-AP and AP-to-hub SPI write messages.

Replace the dynamically allocated RX buffer with a fixed-size,
preallocated buffer embedded in the driver structure and reused for all
SPI receive operations. This removes memory allocation from the
IRQ path, simplifies lifetime management.

Signed-off-by: Sanjay Chitroda <sanjayembeddedse@gmail.com>
---
Changes in v6:
- Replace dynamically allocated RX buffer with embedded fixed-size buffer
- Fix struct layout to satisfy DMA alignment constraints comment from David
- v5 change: https://lore.kernel.org/all/20260406080852.2727453-6-sanjayembedded@gmail.com/
Changes in v5:
- Rebase change on top of latest v5 patch series.
Changes in v4:
- Use preallocated buffer and stash a buffer that gets reused each time instead of a fresh allocation.
- v3 change: https://lore.kernel.org/all/20260315125509.857195-3-sanjayembedded@gmail.com/
Changes in v3:
- prepare series to have all respective cleanup API support for the ssp_sensors following input from Andy Shevchenko
- v2 change: https://lore.kernel.org/all/20260311174151.3441429-1-sanjayembedded@gmail.com/
Changes in v2:
- split series to individual patch
- address review comment from Andy Shevchenko
- v1 change: https://lore.kernel.org/all/20260310200513.2162018-3-sanjayembedded@gmail.com/
---
drivers/iio/common/ssp_sensors/ssp.h | 3 +++
drivers/iio/common/ssp_sensors/ssp_spi.c | 20 ++------------------
2 files changed, 5 insertions(+), 18 deletions(-)

diff --git a/drivers/iio/common/ssp_sensors/ssp.h b/drivers/iio/common/ssp_sensors/ssp.h
index f649cdecc277..8295bb7062a3 100644
--- a/drivers/iio/common/ssp_sensors/ssp.h
+++ b/drivers/iio/common/ssp_sensors/ssp.h
@@ -174,6 +174,7 @@ struct ssp_sensorhub_info {
* @pending_list: pending list for messages queued to be sent/read
* @sensor_devs: registered IIO devices table
* @enable_refcount: enable reference count for wdt (watchdog timer)
+ * @rx_buf: buffer to receive SPI data
* @header_buffer: cache aligned buffer for packet header
*/
struct ssp_data {
@@ -221,6 +222,8 @@ struct ssp_data {
struct iio_dev *sensor_devs[SSP_SENSOR_MAX];
atomic_t enable_refcount;

+ u8 rx_buf[SSP_DATA_PACKET_SIZE];
+
__le16 header_buffer[SSP_HEADER_BUFFER_SIZE / sizeof(__le16)] __aligned(IIO_DMA_MINALIGN);
};

diff --git a/drivers/iio/common/ssp_sensors/ssp_spi.c b/drivers/iio/common/ssp_sensors/ssp_spi.c
index 870214551f0b..e41da88bf96d 100644
--- a/drivers/iio/common/ssp_sensors/ssp_spi.c
+++ b/drivers/iio/common/ssp_sensors/ssp_spi.c
@@ -339,7 +339,7 @@ static int ssp_parse_dataframe(struct ssp_data *data, char *dataframe, int len)
/* threaded irq */
int ssp_irq_msg(struct ssp_data *data)
{
- char *buffer;
+ char *buffer = data->rx_buf;
u8 msg_type;
int ret;
u16 length, msg_options;
@@ -383,19 +383,12 @@ int ssp_irq_msg(struct ssp_data *data)
* but the slave should not send such ones - it is to
* check but let's handle this
*/
- buffer = kmalloc(length, GFP_KERNEL | GFP_DMA);
- if (!buffer) {
- ret = -ENOMEM;
- goto _unlock;
- }

/* got dead packet so it is always an error */
ret = spi_read(data->spi, buffer, length);
if (ret >= 0)
ret = -EPROTO;

- kfree(buffer);
-
dev_err(SSP_DEV, "No match error %x\n",
msg_options);

@@ -428,22 +421,13 @@ int ssp_irq_msg(struct ssp_data *data)
mutex_unlock(&data->pending_lock);
break;
case SSP_HUB2AP_WRITE:
- buffer = kzalloc(length, GFP_KERNEL | GFP_DMA);
- if (!buffer)
- return -ENOMEM;
-
ret = spi_read(data->spi, buffer, length);
if (ret < 0) {
dev_err(SSP_DEV, "spi read fail\n");
- kfree(buffer);
break;
}

- ret = ssp_parse_dataframe(data, buffer, length);
-
- kfree(buffer);
- break;
-
+ return ssp_parse_dataframe(data, buffer, length);
default:
dev_err(SSP_DEV, "unknown msg type\n");
return -EPROTO;
--
2.34.1