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

Jonathan Cameron
2026-04-26T14:35:50Z

On Sun, 26 Apr 2026 14:47:10 +0530
Sanjay Chitroda <sanjayembeddedse@gmail.com> wrote:

> 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>

> 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);
As bellow.

> - 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);
Is there any chance that GFP_DMA marking is needed?

> - if (!buffer)
> - return -ENOMEM;