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

Signed-off-by: Michal Piekos <michal.piekos@mmpsystems.pl>
---
 drivers/iio/adc/sun20i-gpadc-iio.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/iio/adc/sun20i-gpadc-iio.c b/drivers/iio/adc/sun20i-gpadc-iio.c
index 861c14da75ad..95f34a352158 100644
--- a/drivers/iio/adc/sun20i-gpadc-iio.c
+++ b/drivers/iio/adc/sun20i-gpadc-iio.c
@@ -139,8 +139,21 @@ 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)
+{
+	int i;
+
+	for (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: 1d5dcaa3bd65f2e8c9baa14a393d3a2dc5db7524
change-id: 20260513-fix-sunxi-gpadc-sparse-channels-2b6b2063bd49

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

On Wed, 13 May 2026 11:51:31 +0200
Michal Piekos <michal.piekos@mmpsystems.pl> wrote:

> Using consumer driver like iio-hwmon which resolve channels thorugh
> io-channels phandles will fail for sparse channels because IIO core

Can we say the "IIO core by default" does this. Otherwise implication
is we don't provide an alternative - whereas the fwnode_xlate() callback
is there to cover this sort of thing.  Otherwise this sounds like we should
be modifying the IIO core rather than the driver.

Otherwise nothing from me to add to what Andy's already covered.

> threats phandle argument as index into channel array.
>         eg. <&gpadc 1> will fail if there is only channel@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.
> 
> Signed-off-by: Michal Piekos <michal.piekos@mmpsystems.pl>
> ---
>  drivers/iio/adc/sun20i-gpadc-iio.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/iio/adc/sun20i-gpadc-iio.c b/drivers/iio/adc/sun20i-gpadc-iio.c
> index 861c14da75ad..95f34a352158 100644
> --- a/drivers/iio/adc/sun20i-gpadc-iio.c
> +++ b/drivers/iio/adc/sun20i-gpadc-iio.c
> @@ -139,8 +139,21 @@ 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)
> +{
> +	int i;
> +
> +	for (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: 1d5dcaa3bd65f2e8c9baa14a393d3a2dc5db7524
> change-id: 20260513-fix-sunxi-gpadc-sparse-channels-2b6b2063bd49
> 
> Best regards,
> --  
> Michal Piekos <michal.piekos@mmpsystems.pl>
>

On Wed, May 13, 2026 at 11:51:31AM +0200, Michal Piekos wrote:
> Using consumer driver like iio-hwmon which resolve channels thorugh
> io-channels phandles will fail for sparse channels because IIO core
> threats phandle argument as index into channel array.
>         eg. <&gpadc 1> will fail if there is only channel@1 specified
> 
> Add fwnode_xlate which maps DT phandle to the registered channel whose

.fwnode_xlate()

> chan->channel matches the hardware channel number. It allows sparse
> channel maps to be consumed by drivers like iio-hwmon.

...

> +static int sun20i_gpadc_fwnode_xlate(struct iio_dev *indio_dev,
> +		const struct fwnode_reference_args *iiospec)

Broken indentation (I understand the motivation to shift left, but I leave it
to Jonathan on how to proceed with this).

> +{
> +	int i;
> +
> +	for (i = 0; i < indio_dev->num_channels; i++)

	for (unsigned int i = 0; i < indio_dev->num_channels; i++)

> +		if (indio_dev->channels[i].channel == iiospec->args[0])
> +			return i;
> +
> +	return -EINVAL;
> +}

-- 
With Best Regards,
Andy Shevchenko