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Message-ID: <eb9c06de-04e2-427f-9c04-eaaaf4837da6@baylibre.com>
Date: Mon, 18 Aug 2025 10:15:23 -0500
From: David Lechner <dlechner@...libre.com>
To: Ioana Risteiu <Ioana.Risteiu@...log.com>,
Lars-Peter Clausen <lars@...afoo.de>,
Michael Hennerich <Michael.Hennerich@...log.com>,
Jonathan Cameron <jic23@...nel.org>, Nuno Sá
<nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>,
Ramona Nechita <ramona.nechita@...log.com>, linux-iio@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] iio: adc: update ad7779 to use IIO backend
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@...log.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@...log.com>");
> MODULE_DESCRIPTION("Analog Devices AD7779 ADC");
> MODULE_LICENSE("GPL");
> +MODULE_IMPORT_NS("IIO_BACKEND");
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