Re: [PATCH v5 03/10] iio: adc: add helpers for parsing ADC nodes

[David Lechner <dlechner@baylibre.com>]

On Mon, Mar 3, 2025 at 12:32 PM 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.
>
> 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:
> v4 => v5:
> - Inline iio_adc_device_num_channels()
> - Fix Indenting function parameters
> - Combine the max channel ID checks.
> 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
> ---
>  drivers/iio/adc/Kconfig            |  3 ++
>  drivers/iio/adc/Makefile           |  2 +
>  drivers/iio/adc/industrialio-adc.c | 82 ++++++++++++++++++++++++++++++
>  include/linux/iio/adc-helpers.h    | 27 ++++++++++
>  4 files changed, 114 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..7bdae5330224
> --- /dev/null
> +++ b/drivers/iio/adc/industrialio-adc.c
> @@ -0,0 +1,82 @@
> +// 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>
> +
> +/**
> + * 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

s/succes/success/

> + *             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 && ch > max_chan_id)
> +                       return -ERANGE;
> +

Should we use return dev_err_probe() on these to help with debugging a bad dtb?

> +               *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");

We can make this less verbose by setting #define
DEFAULT_SYMBOL_NAMESPACE at the start of the file. Then we can just do
EXPORT_SYMBOL_GPL() throughout the rest of the file.

Also, I would prefer if the namespace matched config name (IIO_ADC_HELPER).

> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Matti Vaittinen <mazziesaccount@gmail.com>");
> +MODULE_DESCRIPTION("IIO ADC fwnode parsing helpers");
> diff --git a/include/linux/iio/adc-helpers.h b/include/linux/iio/adc-helpers.h
> new file mode 100644
> index 000000000000..403a70b109ec
> --- /dev/null
> +++ b/include/linux/iio/adc-helpers.h
> @@ -0,0 +1,27 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +/*
> + * The industrial I/O ADC firmware property parsing helpers
> + *
> + * Copyright (c) 2025 Matti Vaittinen <mazziesaccount@gmail.com>
> + */
> +
> +#ifndef _INDUSTRIAL_IO_ADC_HELPERS_H_
> +#define _INDUSTRIAL_IO_ADC_HELPERS_H_
> +
> +#include <linux/property.h>
> +
> +struct device;
> +struct iio_chan_spec;
> +
> +static inline int iio_adc_device_num_channels(struct device *dev)
> +{
> +       return device_get_child_node_count_named(dev, "channel");
> +}
> +
> +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);
> +

There are some different opinions on this, but on the last patch I did
introducing a new namespace, the consensus seems to be that putting
the MODULE_IMPORT_NS() in the header file was convenient so that users
of the API don't have to remember to both include the header and add
the import macro.

> +#endif /* _INDUSTRIAL_IO_ADC_HELPERS_H_ */
> --
> 2.48.1
>