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

[Jonathan Cameron <jic23@kernel.org>]

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;