[PATCH v3] iio: adc: sun20i-gpadc: support non-contiguous channel lookups

[Michal Piekos]

Using consumer driver like iio-hwmon which resolve channels through
io-channels phandles will fail for sparse channels because IIO core by
default treats phandle argument as index into channel array.
        eg. <&gpadc 1> will fail if there is only channel at 1 specified

Add .fwnode_xlate() which maps DT phandle to the registered channel
whose chan->channel matches the hardware channel number. It allows
sparse channel maps to be consumed by drivers like iio-hwmon.

Tested on Radxa Cubie A5E.

Reviewed-by: Andy Shevchenko <andriy.shevchenko at intel.com>
Signed-off-by: Michal Piekos <michal.piekos at mmpsystems.pl>
---
Changes in v3:
- Add iiospec->nargs validation in sun20i_gpadc_fwnode_xlate()
- Keep Andy's Reviewed-by tag since change is narrow validation fix
- Fix spelling issues in commit message
- Link to v2: https://patch.msgid.link/20260514-fix-sunxi-gpadc-sparse-channels-v2-1-d4a66b70c7a7@mmpsystems.pl

Changes in v2:
- Move loop variable declaration into the for statement
- Fix indentation using clang-format
- Correct commit wording
- Link to v1: https://patch.msgid.link/20260513-fix-sunxi-gpadc-sparse-channels-v1-1-6c21e290bcee@mmpsystems.pl

To: Jonathan Cameron <jic23 at kernel.org>
To: David Lechner <dlechner at baylibre.com>
To: Nuno Sá <nuno.sa at analog.com>
To: Andy Shevchenko <andy at kernel.org>
To: Chen-Yu Tsai <wens at kernel.org>
To: Jernej Skrabec <jernej.skrabec at gmail.com>
To: Samuel Holland <samuel at sholland.org>
To: Nathan Chancellor <nathan at kernel.org>
To: Nick Desaulniers <nick.desaulniers+lkml at gmail.com>
To: Bill Wendling <morbo at google.com>
To: Justin Stitt <justinstitt at google.com>
Cc: linux-iio at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-sunxi at lists.linux.dev
Cc: linux-kernel at vger.kernel.org
Cc: llvm at lists.linux.dev
---
 drivers/iio/adc/sun20i-gpadc-iio.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/iio/adc/sun20i-gpadc-iio.c b/drivers/iio/adc/sun20i-gpadc-iio.c
index 861c14da75ad..8a75498557ff 100644
--- a/drivers/iio/adc/sun20i-gpadc-iio.c
+++ b/drivers/iio/adc/sun20i-gpadc-iio.c
@@ -139,8 +139,23 @@ static irqreturn_t sun20i_gpadc_irq_handler(int irq, void *data)
 	return IRQ_HANDLED;
 }
 
+static int
+sun20i_gpadc_fwnode_xlate(struct iio_dev *indio_dev,
+			  const struct fwnode_reference_args *iiospec)
+{
+	if (iiospec->nargs != 1)
+		return -EINVAL;
+
+	for (unsigned int i = 0; i < indio_dev->num_channels; i++)
+		if (indio_dev->channels[i].channel == iiospec->args[0])
+			return i;
+
+	return -EINVAL;
+}
+
 static const struct iio_info sun20i_gpadc_iio_info = {
 	.read_raw = sun20i_gpadc_read_raw,
+	.fwnode_xlate = sun20i_gpadc_fwnode_xlate,
 };
 
 static void sun20i_gpadc_reset_assert(void *data)

---
base-commit: 6916d5703ddf9a38f1f6c2cc793381a24ee914c6
change-id: 20260513-fix-sunxi-gpadc-sparse-channels-2b6b2063bd49

Best regards,
--  
Michal Piekos <michal.piekos at mmpsystems.pl>