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

Matti Vaittinen
2025-02-24T18:33:23Z

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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:
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);
+
+/**
+ * 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;
+
+ *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");
diff --git a/include/linux/iio/adc-helpers.h b/include/linux/iio/adc-helpers.h
new file mode 100644
index 000000000000..5d64244f1552
--- /dev/null
+++ b/include/linux/iio/adc-helpers.h
@@ -0,0 +1,22 @@
+/* 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_
+
+struct device;
+struct fwnode_handle;
+struct iio_chan_spec;
+
+int iio_adc_device_num_channels(struct device *dev);
+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);
+
+#endif /* _INDUSTRIAL_IO_ADC_HELPERS_H_ */
--
2.48.1

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