Re: [PATCH v4 03/10] iio: adc: add helpers for parsing ADC nodes

Jonathan Cameron
2025-03-02T03:35:30Z

On Mon, 24 Feb 2025 20:33:16 +0200
Matti Vaittinen <mazziesaccount@gmail.com> wrote:

> There are ADC ICs which may have some of the AIN pins usable for other
> functions. These ICs may have some of the AIN pins wired so that they
> should not be used for ADC.
>
> (Preferred?) way for marking pins which can be used as ADC inputs is to
> add corresponding channels@N nodes in the device tree as described in
> the ADC binding yaml.
I think it's worth exploring if we can tweak this slightly to make
that something a driver specifies. Either skip the unspecified or
fill them with default values depending on a parameter.

Would make this code cover the existing cases better.
Might be a little fiddly as we'd want to maintain ordering so
the code would need to index slightly differently. I've not tried it
so maybe not worth it for now.

>
> Add couple of helper functions which can be used to retrieve the channel
> information from the device node.
>
> Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
>
> ---
> Revision history:
> v3 => v4:
> - Drop diff-channel support
> - Drop iio_adc_device_channels_by_property()
> - Add IIO_DEVICE namespace
> - Move industrialio-adc.o to top of the Makefile
> - Some styling as suggested by Andy
> - Re-consider included headers
> v2 => v3: Mostly based on review comments by Jonathan
> - Support differential and single-ended channels
> - Rename iio_adc_device_get_channels() as
> iio_adc_device_channels_by_property()
> - Improve spelling
> - Drop support for cases where DT comes from parent device's node
> - Decrease loop indent by reverting node name check conditions
> - Don't set 'chan->indexed' by number of channels to keep the
> interface consistent no matter how many channels are connected.
> - Fix ID range check and related comment
> RFC v1 => v2:
> - New patch
>
> iio: adc: helper: drop headers
> ---
> drivers/iio/adc/Kconfig | 3 +
> drivers/iio/adc/Makefile | 2 +
> drivers/iio/adc/industrialio-adc.c | 89 ++++++++++++++++++++++++++++++
> include/linux/iio/adc-helpers.h | 22 ++++++++
> 4 files changed, 116 insertions(+)
> create mode 100644 drivers/iio/adc/industrialio-adc.c
> create mode 100644 include/linux/iio/adc-helpers.h
>
> diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> index 849c90203071..37b70a65da6f 100644
> --- a/drivers/iio/adc/Kconfig
> +++ b/drivers/iio/adc/Kconfig
> @@ -6,6 +6,9 @@
>
> menu "Analog to digital converters"
>
> +config IIO_ADC_HELPER
> + tristate
> +
> config AB8500_GPADC
> bool "ST-Ericsson AB8500 GPADC driver"
> depends on AB8500_CORE && REGULATOR_AB8500
> diff --git a/drivers/iio/adc/Makefile b/drivers/iio/adc/Makefile
> index ee19afba62b7..1c410f483029 100644
> --- a/drivers/iio/adc/Makefile
> +++ b/drivers/iio/adc/Makefile
> @@ -3,6 +3,8 @@
> # Makefile for IIO ADC drivers
> #
>
> +obj-$(CONFIG_IIO_ADC_HELPER) += industrialio-adc.o
> +
> # When adding new entries keep the list in alphabetical order
> obj-$(CONFIG_AB8500_GPADC) += ab8500-gpadc.o
> obj-$(CONFIG_AD_SIGMA_DELTA) += ad_sigma_delta.o
> diff --git a/drivers/iio/adc/industrialio-adc.c b/drivers/iio/adc/industrialio-adc.c
> new file mode 100644
> index 000000000000..d8e9e6825d2b
> --- /dev/null
> +++ b/drivers/iio/adc/industrialio-adc.c
> @@ -0,0 +1,89 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Helpers for parsing common ADC information from a firmware node.
> + *
> + * Copyright (c) 2025 Matti Vaittinen <mazziesaccount@gmail.com>
> + */
> +
> +#include <linux/device.h>
> +#include <linux/errno.h>
> +#include <linux/export.h>
> +#include <linux/module.h>
> +#include <linux/property.h>
> +#include <linux/types.h>
> +
> +#include <linux/iio/adc-helpers.h>
> +#include <linux/iio/iio.h>
> +
> +int iio_adc_device_num_channels(struct device *dev)
> +{
> + return device_get_child_node_count_named(dev, "channel");
> +}
> +EXPORT_SYMBOL_GPL(iio_adc_device_num_channels);

Maybe one to promote to a static inline in the header and avoid need for
the export given it is very simple.

> +
> +/**
> + * devm_iio_adc_device_alloc_chaninfo_se - allocate and fill iio_chan_spec for ADC
> + *
> + * Scan the device node for single-ended ADC channel information. Channel ID is
> + * expected to be found from the "reg" property. Allocate and populate the
> + * iio_chan_spec structure corresponding to channels that are found. The memory
> + * for iio_chan_spec structure will be freed upon device detach.
> + *
> + * @dev: Pointer to the ADC device.
> + * @template: Template iio_chan_spec from which the fields of all
> + * found and allocated channels are initialized.
> + * @max_chan_id: Maximum value of a channel ID. Use -1 if no checking
> + * is required.
> + * @cs: Location where pointer to allocated iio_chan_spec
> + * should be stored.
> + *
> + * Return: Number of found channels on succes. Negative value to indicate
> + * failure.
> + */
> +int devm_iio_adc_device_alloc_chaninfo_se(struct device *dev,
> + const struct iio_chan_spec *template,
> + int max_chan_id,
> + struct iio_chan_spec **cs)
> +{
> + struct iio_chan_spec *chan_array, *chan;
> + int num_chan = 0, ret;
> +
> + num_chan = iio_adc_device_num_channels(dev);
> + if (num_chan < 1)
> + return num_chan;
> +
> + chan_array = devm_kcalloc(dev, num_chan, sizeof(*chan_array),
> + GFP_KERNEL);
> + if (!chan_array)
> + return -ENOMEM;
> +
> + chan = &chan_array[0];
> +
> + device_for_each_child_node_scoped(dev, child) {
> + u32 ch;
> +
> + if (!fwnode_name_eq(child, "channel"))
> + continue;
> +
> + ret = fwnode_property_read_u32(child, "reg", &ch);
> + if (ret)
> + return ret;
> +
> + if (max_chan_id != -1)
> + if (ch > max_chan_id)
> + return -ERANGE;

Might as well combine.
if (max_chan_id != -1 && ch > max_chan_id)
return -ERANGE;
> +
> + *chan = *template;
> + chan->channel = ch;
> + chan++;
> + }
> +
> + *cs = chan_array;
> +
> + return num_chan;
> +}
> +EXPORT_SYMBOL_NS_GPL(devm_iio_adc_device_alloc_chaninfo_se, "IIO_DRIVER");
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Matti Vaittinen <mazziesaccount@gmail.com>");
> +MODULE_DESCRIPTION("IIO ADC fwnode parsing helpers");