Re: [PATCH v3 4/4] iio: adc: update ad7779 to use IIO backend

[David Lechner <dlechner@baylibre.com>]

On 8/18/25 8:12 AM, Ioana Risteiu wrote:
> Add a new functionality to ad7779 driver that streams data through data
> output interface using IIO backend interface.
> 
> Signed-off-by: Ioana Risteiu <Ioana.Risteiu@analog.com>
> ---
>  drivers/iio/adc/ad7779.c | 107 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 106 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/ad7779.c b/drivers/iio/adc/ad7779.c
> index f7e681c0e8c0..abf3fff20dd4 100644
> --- a/drivers/iio/adc/ad7779.c
> +++ b/drivers/iio/adc/ad7779.c
> @@ -31,6 +31,8 @@
>  #include <linux/iio/triggered_buffer.h>
>  #include <linux/iio/trigger_consumer.h>
>  
> +#include <linux/iio/backend.h>

This should be grouped in alphabetical order with other
linux/iio/ includes.

> +
>  #define AD7779_SPI_READ_CMD			BIT(7)
>  
>  #define AD7779_DISABLE_SD			BIT(7)
> @@ -157,6 +159,8 @@ struct ad7779_state {
>  	u8			reg_rx_buf[3];
>  	u8			reg_tx_buf[3];
>  	u8			reset_buf[8];
> +
> +	struct iio_backend *back;

This field needs to be placed in the struct before
__aligned(IIO_DMA_MINALIGN) to avoid issues cache lines.

>  };
>  
>  static const char * const ad7779_filter_type[] = {
> @@ -630,12 +634,38 @@ static int ad7779_reset(struct iio_dev *indio_dev, struct gpio_desc *reset_gpio)
>  	return ret;
>  }
>  
> +static int ad7779_update_scan_mode(struct iio_dev *indio_dev,
> +				   const unsigned long *scan_mask)
> +{
> +	struct ad7779_state *st = iio_priv(indio_dev);
> +	unsigned int c;
> +	int ret;
> +
> +	for (c = 0; c < AD7779_NUM_CHANNELS; c++) {
> +		if (test_bit(c, scan_mask))
> +			ret = iio_backend_chan_enable(st->back, c);
> +		else
> +			ret = iio_backend_chan_disable(st->back, c);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
>  static const struct iio_info ad7779_info = {
>  	.read_raw = ad7779_read_raw,
>  	.write_raw = ad7779_write_raw,
>  	.debugfs_reg_access = &ad7779_reg_access,
>  };
>  
> +static const struct iio_info ad7779_info_data = {
> +	.read_raw = ad7779_read_raw,
> +	.write_raw = ad7779_write_raw,
> +	.debugfs_reg_access = &ad7779_reg_access,
> +	.update_scan_mode = &ad7779_update_scan_mode,
> +};
> +
>  static const struct iio_enum ad7779_filter_enum = {
>  	.items = ad7779_filter_type,
>  	.num_items = ARRAY_SIZE(ad7779_filter_type),
> @@ -674,6 +704,7 @@ static const struct iio_chan_spec_ext_info ad7779_ext_filter[] = {
>  
>  #define AD777x_CHAN_FILTER_S(index)					\
>  	AD777x_CHAN_S(index, ad7779_ext_filter)
> +

Unrelated blank line add (should not be in this patch).

>  static const struct iio_chan_spec ad7779_channels[] = {
>  	AD777x_CHAN_NO_FILTER_S(0),
>  	AD777x_CHAN_NO_FILTER_S(1),
> @@ -752,6 +783,44 @@ static int ad7779_conf(struct ad7779_state *st, struct gpio_desc *start_gpio)
>  	return 0;
>  }
>  
> +static int ad7779_set_data_lines(struct iio_dev *indio_dev,
> +				 unsigned int num_lanes)
> +{
> +	struct ad7779_state *st = iio_priv(indio_dev);
> +	int ret;
> +
> +	ret = ad7779_set_sampling_frequency(st, num_lanes * AD7779_DEFAULT_SAMPLING_1LINE);
> +	if (ret)
> +		return ret;
> +
> +	ret = iio_backend_num_lanes_set(st->back, num_lanes);
> +	if (ret)
> +		return ret;
> +
> +	return ad7779_spi_write_mask(st, AD7779_REG_DOUT_FORMAT,
> +				    AD7779_DOUT_FORMAT_MSK,
> +				    FIELD_PREP(AD7779_DOUT_FORMAT_MSK, 2 - ilog2(num_lanes)));
> +}
> +
> +static int ad7779_setup_channels(struct iio_dev *indio_dev, const struct ad7779_state *st)
> +{
> +	struct iio_chan_spec *channels;
> +	struct device *dev = &st->spi->dev;
> +
> +	channels = devm_kmemdup_array(dev, st->chip_info->channels,
> +					ARRAY_SIZE(ad7779_channels),
> +					sizeof(*channels), GFP_KERNEL);
> +	if (!channels)
> +		return -ENOMEM;
> +
> +	for (int i = 0; i < ARRAY_SIZE(ad7779_channels); i++)
> +		channels[i].scan_type.endianness = IIO_CPU;
> +
> +	indio_dev->channels = channels;
> +
> +	return 0;
> +}
> +
>  static int ad7779_setup_without_backend(struct ad7779_state *st, struct iio_dev *indio_dev)
>  {
>  	int ret;
> @@ -796,6 +865,38 @@ static int ad7779_setup_without_backend(struct ad7779_state *st, struct iio_dev
>  				    FIELD_PREP(AD7779_DCLK_CLK_DIV_MSK, 7));
>  }
>  
> +static int ad7779_setup_backend(struct ad7779_state *st, struct iio_dev *indio_dev)
> +{
> +	struct device *dev = &st->spi->dev;
> +	int ret = -EINVAL;
> +	int num_lanes;
> +
> +	indio_dev->info = &ad7779_info_data;
> +
> +	ret = ad7779_setup_channels(indio_dev, st);
> +	if (ret)
> +		return ret;
> +
> +	st->back = devm_iio_backend_get(dev, NULL);
> +	if (IS_ERR(st->back))
> +		return dev_err_probe(dev, PTR_ERR(st->back),
> +				     "failed to get iio backend");
> +
> +	ret = devm_iio_backend_request_buffer(dev, st->back, indio_dev);
> +	if (ret)
> +		return ret;
> +
> +	ret = devm_iio_backend_enable(dev, st->back);
> +	if (ret)
> +		return ret;
> +

The usual way of doing this is to set num_lanes = 4 here.

> +	ret = device_property_read_u32(dev, "adi,num-lanes", &num_lanes);
> +	if (ret)

It is best to not ignore all errors. So typically, we would have

	if (ret && ret != -EINVAL)
		return ret;

here. In the -EINVAL case, the default we set above will be used.

We should also validate that the value is 1, 2 or 4 so that later
calculations that use this are valid.

> +		return ad7779_set_data_lines(indio_dev, 4);
> +
> +	return ad7779_set_data_lines(indio_dev, num_lanes);

Then we don't have to have 2 calls to the same function.

> +}
> +
>  static int ad7779_probe(struct spi_device *spi)
>  {
>  	struct iio_dev *indio_dev;
> @@ -848,7 +949,10 @@ static int ad7779_probe(struct spi_device *spi)
>  	indio_dev->modes = INDIO_DIRECT_MODE;
>  	indio_dev->num_channels = ARRAY_SIZE(ad7779_channels);
>  
> -	ret = ad7779_setup_without_backend(st, indio_dev);
> +	if (device_property_present(dev, "io-backends"))
> +		ret = ad7779_setup_backend(st, indio_dev);
> +	else
> +		ret = ad7779_setup_without_backend(st, indio_dev);
>  
>  	if (ret)
>  		return ret;
> @@ -943,3 +1047,4 @@ module_spi_driver(ad7779_driver);
>  MODULE_AUTHOR("Ramona Alexandra Nechita <ramona.nechita@analog.com>");
>  MODULE_DESCRIPTION("Analog Devices AD7779 ADC");
>  MODULE_LICENSE("GPL");
> +MODULE_IMPORT_NS("IIO_BACKEND");