Re: [PATCH v2 4/4] iio: adc: ad7768-1: add support for SPI offload

[David Lechner <dlechner@baylibre.com>]

On 2/23/26 5:59 AM, Jonathan Santos wrote:
> The AD7768-1 family supports sampling rates up to 1 MSPS, which exceeds
> the capabilities of conventional triggered buffer operations due to SPI
> transaction overhead and interrupt latency.
> 

...

> +static int ad7768_offload_buffer_postenable(struct iio_dev *indio_dev)
> +{
> +	struct ad7768_state *st = iio_priv(indio_dev);
> +	struct spi_offload_trigger_config config = {
> +		.type = SPI_OFFLOAD_TRIGGER_DATA_READY,
> +	};
> +	const struct iio_scan_type *scan_type;
> +	unsigned int unused;
> +	int ret;
> +
> +	scan_type = iio_get_current_scan_type(indio_dev, &indio_dev->channels[0]);
> +	if (IS_ERR(scan_type))
> +		return PTR_ERR(scan_type);
> +
> +	st->offload_xfer.len = spi_bpw_to_bytes(scan_type->realbits);
> +	st->offload_xfer.bits_per_word = scan_type->realbits;
> +	st->offload_xfer.offload_flags = SPI_OFFLOAD_XFER_RX_STREAM;
> +
> +	spi_message_init_with_transfers(&st->offload_msg, &st->offload_xfer, 1);
> +	st->offload_msg.offload = st->offload;
> +
> +	ret = spi_optimize_message(st->spi, &st->offload_msg);
> +	if (ret) {
> +		dev_err(&st->spi->dev, "failed to prepare offload, err: %d\n", ret);
> +		return ret;
> +	}
> +
> +	/*
> +	 * Write a 1 to the LSB of the INTERFACE_FORMAT register to enter
> +	 * continuous read mode. Subsequent data reads do not require an
> +	 * initial 8-bit write to query the ADC_DATA register.
> +	 */
> +	ret =  regmap_write(st->regmap, AD7768_REG_INTERFACE_FORMAT, 0x01);
> +	if (ret)
> +		goto err_unoptimize_message;
> +
> +	ret = spi_offload_trigger_enable(st->offload, st->offload_trigger,
> +					 &config);
> +	if (ret)
> +		goto err_exit_continuous_read_mode;
> +
> +	return 0;
> +
> +err_exit_continuous_read_mode:

I wouldn't mind a comment here explaining what this read does.

> +	regmap_read(st->regmap24, AD7768_REG24_ADC_DATA, &unused);
> +
> +err_unoptimize_message:
> +	spi_unoptimize_message(&st->offload_msg);
> +
> +	return ret;
> +}

...

> +static bool ad7768_offload_trigger_match(struct spi_offload_trigger *trigger,
> +					 enum spi_offload_trigger_type type,
> +					 u64 *args, u32 nargs)
> +{
> +	if (type != SPI_OFFLOAD_TRIGGER_DATA_READY)
> +		return false;
> +
> +	/* Requires 1 or 2 args to indicate the trigger output signal */

Would be more clear to say "up to 2 args are allowed, but only 1 is used".

> +	if (nargs == 0 || nargs > 2 || args[0] != AD7768_TRIGGER_SOURCE_DRDY)
> +		return false;
> +
> +	return true;
> +}
> +