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

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 28 Feb 2026 11:18:22 -0600
David Lechner <dlechner@baylibre.com> wrote:

> 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.

Given I'm not sure, Jonathan, can we have such a comment as a follow up patch please.
> 
> > +	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".
I tweaked this.

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