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Message-ID: <20260131181939.29b35a98@jic23-huawei>
Date: Sat, 31 Jan 2026 18:19:39 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Antoniu Miclaus <antoniu.miclaus@...log.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich
<Michael.Hennerich@...log.com>, David Lechner <dlechner@...libre.com>, 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>, <linux-iio@...r.kernel.org>,
<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] iio: adc: ad4080: add support for AD4880
dual-channel ADC
On Thu, 29 Jan 2026 17:27:30 +0200
Antoniu Miclaus <antoniu.miclaus@...log.com> wrote:
> Add support for the AD4880, a dual-channel 20-bit 40MSPS SAR ADC with
> integrated fully differential amplifiers (FDA).
>
> The AD4880 has two independent ADC channels, each with its own SPI
> configuration interface. The driver uses spi_new_ancillary_device() to
> create an additional SPI device for the second channel, allowing both
> channels to share the same SPI bus with different chip selects.
>
> Key changes:
> - Add AD4880 chip info with 2 channels
> - Extend state structure to support arrays of regmaps and backends
> - Refactor setup into per-channel function
> - Add adi,aux-spi-cs property for secondary channel chip select
> - Add channel index parameter to channel macro for scan_index support
> - Make all IIO attributes per-channel (filter_type, oversampling_ratio,
> sampling_frequency) for independent channel configuration
>
> Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
Hi Antoniu
A few additional comments from me to add to those of the other reviewers.
Jonathan
> ---
> drivers/iio/adc/ad4080.c | 236 ++++++++++++++++++++++++++++-----------
> 1 file changed, 172 insertions(+), 64 deletions(-)
>
> diff --git a/drivers/iio/adc/ad4080.c b/drivers/iio/adc/ad4080.c
> index 7cf3b6ed7940..e588ff23a7a5 100644
> --- a/drivers/iio/adc/ad4080.c
> +++ b/drivers/iio/adc/ad4080.c
> static int ad4080_probe(struct spi_device *spi)
> {
> + static const char * const backend_names[] = { "0", "1" };
> struct iio_dev *indio_dev;
> struct device *dev = &spi->dev;
> struct ad4080_state *st;
> struct clk *clk;
> + unsigned int ch;
> int ret;
>
> indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
> @@ -610,6 +683,10 @@ static int ad4080_probe(struct spi_device *spi)
>
> st = iio_priv(indio_dev);
>
> + st->info = spi_get_device_match_data(spi);
> + if (!st->info)
> + return -ENODEV;
> +
> ret = devm_regulator_bulk_get_enable(dev,
> ARRAY_SIZE(ad4080_power_supplies),
> ad4080_power_supplies);
> @@ -617,13 +694,35 @@ static int ad4080_probe(struct spi_device *spi)
> return dev_err_probe(dev, ret,
> "failed to get and enable supplies\n");
>
> - st->regmap = devm_regmap_init_spi(spi, &ad4080_regmap_config);
> - if (IS_ERR(st->regmap))
> - return PTR_ERR(st->regmap);
> + /* Setup primary SPI device (channel 0) */
> + st->spi[0] = spi;
> + st->regmap[0] = devm_regmap_init_spi(spi, &ad4080_regmap_config);
> + if (IS_ERR(st->regmap[0]))
> + return PTR_ERR(st->regmap[0]);
>
> - st->info = spi_get_device_match_data(spi);
> - if (!st->info)
> - return -ENODEV;
> + /* Setup ancillary SPI device for additional channel (AD4880) */
> + if (st->info->num_channels > 1) {
This hard codes assumption that it is 2. So perhaps better to check for
that explicitly rather than simply > 1.
Maybe turn this into an appropriate loop so you don't need to care that
it's 2 or bigger.
> + u32 aux_cs;
> +
> + ret = device_property_read_u32(dev, "adi,aux-spi-cs", &aux_cs);
> + if (ret)
> + return dev_err_probe(dev, ret,
> + "missing adi,aux-spi-cs for multi-channel device\n");
> +
> + st->spi[1] = spi_new_ancillary_device(spi, aux_cs);
> + if (IS_ERR(st->spi[1]))
> + return PTR_ERR(st->spi[1]);
> +
> + ret = devm_add_action_or_reset(dev, ad4080_unregister_ancillary,
> + st->spi[1]);
> + if (ret)
> + return ret;
> +
> + st->regmap[1] = devm_regmap_init_spi(st->spi[1],
> + &ad4080_regmap_config);
> + if (IS_ERR(st->regmap[1]))
> + return PTR_ERR(st->regmap[1]);
> + }
>
> ret = devm_mutex_init(dev, &st->lock);
> if (ret)
> @@ -644,15 +743,22 @@ static int ad4080_probe(struct spi_device *spi)
>
> st->clk_rate = clk_get_rate(clk);
>
> - st->back = devm_iio_backend_get(dev, NULL);
> - if (IS_ERR(st->back))
> - return PTR_ERR(st->back);
> + /* Get backends for all channels */
> + for (ch = 0; ch < st->info->num_channels; ch++) {
> + if (st->info->num_channels > 1)
> + st->back[ch] = devm_iio_backend_get(dev, backend_names[ch]);
> + else
> + st->back[ch] = devm_iio_backend_get(dev, NULL);
To me, it makes sense to always use names for multi channel devices and only
fall back to this if there is only one supported channel.
Something like
char *name = NULL;
if (st->info->num_channels != 1)
name = backend_names[ch];
st->back[ch] = devm_iio_backend_get(dev, name);
>
> - ret = devm_iio_backend_request_buffer(dev, st->back, indio_dev);
> - if (ret)
> - return ret;
> + if (IS_ERR(st->back[ch]))
> + return PTR_ERR(st->back[ch]);
> +
> + ret = devm_iio_backend_enable(dev, st->back[ch]);
This changes the ordering so we now enable it before requesting the buffer.
That may well be fine, but I'd kind of prefer that to be made clear. Perhaps
with a precursor patch reorganizing that order where you can talk about why
it is fine to do so.
> + if (ret)
> + return ret;
> + }
>
> - ret = devm_iio_backend_enable(dev, st->back);
> + ret = devm_iio_backend_request_buffer(dev, st->back[0], indio_dev);
Add a comment on why requesting only the first buffer is enough.
> if (ret)
> return ret;
>
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