Re: [PATCH v4 4/4] iio: ssp_sensors: reuse preallocated RX buffer for SPI transfers

[Andy Shevchenko]

On Thu, Mar 26, 2026 at 01:48:15PM +0530, Sanjay Chitroda wrote:

> Avoid allocating a temporary DMA buffer in the interrupt context when
> handling hub-to-AP and AP-to-hub SPI write messages.
> 
> Preallocate RX buffer during probe and reuse it for SPI receive
> operations. This removes repeated kzalloc() calls from the IRQ
> path, reduces allocation overhead, and avoids potential allocation
> failures under memory pressure.
> 
> The RX buffer size is tracked and allocated using devm_kzalloc(), ensuring
> proper lifetime management tied to the device.
> 
> No functional change intended; this is an internal optimization and
> robustness improvement.

NAK.

...

> @@ -512,6 +512,17 @@ static int ssp_probe(struct spi_device *spi)
>  
>  	mutex_init(&data->comm_lock);

Pzzz! The wrong use of managed vs. unmanaged resources.

> +	data->rx_buf_size = SSP_DATA_PACKET_SIZE;
> +	data->rx_buf = devm_kzalloc(&spi->dev,
> +				    data->rx_buf_size,
> +				    GFP_KERNEL | GFP_DMA);

There are plenty of room on the previous lines. I think I already commented on
something like this.

> +

This blank line is redundant.

> +	if (!data->rx_buf) {

> +		dev_err(&spi->dev,
> +			"Failed to allocate memory for rx_buf\n");

Pzzz!
Have you read about error messages for -ENOMEM? Please, take your time and
study this case.

> +		return -ENOMEM;
> +	}
> +
>  	for (i = 0; i < SSP_SENSOR_MAX; ++i) {
>  		data->delay_buf[i] = SSP_DEFAULT_POLLING_DELAY;
>  		data->batch_latency_buf[i] = 0;


-- 
With Best Regards,
Andy Shevchenko