[PATCH v4 05/10] iio: adc: sun20i-gpadc: Use adc-helpers

Matti Vaittinen
2025-02-24T18:33:54Z

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The new devm_iio_adc_device_alloc_chaninfo() -helper is intended to help
drivers avoid open-coding the for_each_node -loop for getting the
channel IDs. The helper provides standard way to detect the ADC channel
nodes (by the node name), and a standard way to convert the "reg",
"diff-channels", "single-channel" and the "common-mode-channel" to
channel identification numbers used in the struct iio_chan_spec.
Furthermore, the helper checks the ID is in range of 0 ... num-channels.

The original driver treated all found child nodes as channel nodes. The
new helper requires channel nodes to be named channel[@N]. This should
help avoid problems with devices which may contain also other but ADC
child nodes. Quick grep from arch/* with the sun20i-gpadc's compatible
string didn't reveal any in-tree .dts with channel nodes named
othervice. Also, same grep shows all the in-tree .dts seem to have
channel IDs between 0..num of channels.

Use the new helper.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>

---
Revision history:
v3 => v4:
- Adapt to 'drop diff-channel support' changes to ADC-helpers
- select ADC helpers in the Kconfig
v2 => v3:
- New patch

I picked the sun20i-gpadc in this series because it has a straightforward
approach for populating the struct iio_chan_spec. Everything else except
the .channel can use 'template'-data.

This makes the sun20i-gpadc well suited to be an example user of this new
helper. I hope this patch helps to evaluate whether these helpers are worth
the hassle.

The change is compile tested only!! Testing before applying is highly
appreciated (as always!). Also, even though I tried to audit the dts
files for the reg-properties in the channel nodes, use of references
didn't make it easy. I can't guarantee I didn't miss anything.
---
drivers/iio/adc/Kconfig | 1 +
drivers/iio/adc/sun20i-gpadc-iio.c | 38 ++++++++++++------------------
2 files changed, 16 insertions(+), 23 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index e4933de0c366..0993008a1586 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -1357,6 +1357,7 @@ config SUN4I_GPADC
config SUN20I_GPADC
tristate "Allwinner D1/T113s/T507/R329 and similar GPADCs driver"
depends on ARCH_SUNXI || COMPILE_TEST
+ select IIO_ADC_HELPER
help
Say yes here to build support for Allwinner (D1, T113, T507 and R329)
SoCs GPADC. This ADC provides up to 16 channels.
diff --git a/drivers/iio/adc/sun20i-gpadc-iio.c b/drivers/iio/adc/sun20i-gpadc-iio.c
index 136b8d9c294f..bf1db2a3de9b 100644
--- a/drivers/iio/adc/sun20i-gpadc-iio.c
+++ b/drivers/iio/adc/sun20i-gpadc-iio.c
@@ -15,6 +15,7 @@
#include <linux/property.h>
#include <linux/reset.h>

+#include <linux/iio/adc-helpers.h>
#include <linux/iio/iio.h>

#define SUN20I_GPADC_DRIVER_NAME "sun20i-gpadc"
@@ -149,37 +150,27 @@ static void sun20i_gpadc_reset_assert(void *data)
reset_control_assert(rst);
}

+static const struct iio_chan_spec sun20i_gpadc_chan_template = {
+ .type = IIO_VOLTAGE,
+ .indexed = 1,
+ .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+ .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
+};
+
static int sun20i_gpadc_alloc_channels(struct iio_dev *indio_dev,
struct device *dev)
{
- unsigned int channel;
- int num_channels, i, ret;
+ int num_channels;
struct iio_chan_spec *channels;

- num_channels = device_get_child_node_count(dev);
+ num_channels = devm_iio_adc_device_alloc_chaninfo_se(dev,
+ &sun20i_gpadc_chan_template, -1, &channels);
+ if (num_channels < 0)
+ return num_channels;
+
if (num_channels == 0)
return dev_err_probe(dev, -ENODEV, "no channel children\n");

- channels = devm_kcalloc(dev, num_channels, sizeof(*channels),
- GFP_KERNEL);
- if (!channels)
- return -ENOMEM;
-
- i = 0;
- device_for_each_child_node_scoped(dev, node) {
- ret = fwnode_property_read_u32(node, "reg", &channel);
- if (ret)
- return dev_err_probe(dev, ret, "invalid channel number\n");
-
- channels[i].type = IIO_VOLTAGE;
- channels[i].indexed = 1;
- channels[i].channel = channel;
- channels[i].info_mask_separate = BIT(IIO_CHAN_INFO_RAW);
- channels[i].info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE);
-
- i++;
- }
-
indio_dev->channels = channels;
indio_dev->num_channels = num_channels;

@@ -271,3 +262,4 @@ module_platform_driver(sun20i_gpadc_driver);
MODULE_DESCRIPTION("ADC driver for sunxi platforms");
MODULE_AUTHOR("Maksim Kiselev <bigunclemax@gmail.com>");
MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS("IIO_DRIVER");
--
2.48.1

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