[PATCH] iio: adc: stm32-adc: fix check on internal channel availability

[Fabrice Gasnier]

If an unsupported internal channel like vddgpu is requested, the driver
prints a warning but falls through and assigns it a valid int_ch below.

This causes a problem later during setup:
stm32_adc_int_ch_enable() {
    ...
    case STM32_ADC_INT_CH_VDDGPU:
        stm32_adc_set_bits(adc, adc->cfg->regs->or_vddgpu.reg,
                           adc->cfg->regs->or_vddgpu.mask);
    ...
}

Because the register offset is uninitialized (0), this performs a
read-modify-write on offset 0, which corresponds to the ISR register.

Fix this by returning before a valid int_ch is assigned.
Choice is made to just warn about the channel name as it could
be confusing, rather than making the probe fail.

Fixes: cf0fb80ae167 ("iio: adc: stm32-adc: add stm32mp13 support")
Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
Link: https://lore.kernel.org/all/20260911162602.D323F1F000FF@xxxxxxxxxxxxxxx/
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxxxxxxx>
---
 drivers/iio/adc/stm32-adc.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
index 5c6c06b269be..87fafdd4698b 100644
--- a/drivers/iio/adc/stm32-adc.c
+++ b/drivers/iio/adc/stm32-adc.c
@@ -2259,7 +2259,7 @@ static int stm32_adc_populate_int_ch(struct iio_dev *indio_dev, const char *ch_n
 {
 	struct stm32_adc *adc = iio_priv(indio_dev);
 	u16 vrefint;
-	int i, ret;
+	int i, ret = 0;
 
 	for (i = 0; i < STM32_ADC_INT_CH_NB; i++) {
 		if (!strncmp(stm32_adc_ic[i].name, ch_name, STM32_ADC_CH_SZ)) {
@@ -2267,31 +2267,36 @@ static int stm32_adc_populate_int_ch(struct iio_dev *indio_dev, const char *ch_n
 			switch (i) {
 			case STM32_ADC_INT_CH_VDDCORE:
 				if (!adc->cfg->regs->or_vddcore.reg)
-					dev_warn(&indio_dev->dev,
-						 "%s channel not available\n", ch_name);
+					ret = -ENOENT;
 				break;
 			case STM32_ADC_INT_CH_VDDCPU:
 				if (!adc->cfg->regs->or_vddcpu.reg)
-					dev_warn(&indio_dev->dev,
-						 "%s channel not available\n", ch_name);
+					ret = -ENOENT;
 				break;
 			case STM32_ADC_INT_CH_VDDQ_DDR:
 				if (!adc->cfg->regs->or_vddq_ddr.reg)
-					dev_warn(&indio_dev->dev,
-						 "%s channel not available\n", ch_name);
+					ret = -ENOENT;
 				break;
 			case STM32_ADC_INT_CH_VREFINT:
 				if (!adc->cfg->regs->ccr_vref.reg)
-					dev_warn(&indio_dev->dev,
-						 "%s channel not available\n", ch_name);
+					ret = -ENOENT;
 				break;
 			case STM32_ADC_INT_CH_VBAT:
 				if (!adc->cfg->regs->ccr_vbat.reg)
-					dev_warn(&indio_dev->dev,
-						 "%s channel not available\n", ch_name);
+					ret = -ENOENT;
 				break;
 			}
 
+			if (ret) {
+				/*
+				 * Confusing channel label matches an internal STM32 ADC channel.
+				 * Just warn about it, as there's normally no restriction on the
+				 * name but that's not among supported internal channels.
+				 */
+				dev_warn(&indio_dev->dev, "no %s internal channel\n", ch_name);
+				return 0;
+			}
+
 			if (stm32_adc_ic[i].idx != STM32_ADC_INT_CH_VREFINT) {
 				adc->int_ch[i] = chan;
 				break;

---
base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
change-id: 20260915-adc-fix-intchan-v1-3deda8cecb50

Best regards,
--  
Fabrice Gasnier <fabrice.gasnier@xxxxxxxxxxx>