[PATCH v3] 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 keep current driver behavior to warn about the channel name.

Fixes: cf0fb80ae167 ("iio: adc: stm32-adc: add stm32mp13 support")
Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
Closes: https://lore.kernel.org/all/20260911162602.D323F1F000FF@xxxxxxxxxxxxxxx/
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxxxxxxx>
---
Changes in v3:
- Comment from Andy: use Closes instead of Link in the commit message
- Add collected Andy's Reviewed-by
- Link to v2: https://patch.msgid.link/20260916-adc-fix-intchan-v1-v2-1-ef70baecd082@xxxxxxxxxxx

Changes in v2:
- Review comments from Andy: use bool flag closer to the channel
  availabilty checks. Add a default case.
- Link to v1: https://patch.msgid.link/20260915-adc-fix-intchan-v1-v1-1-761a1b35001b@xxxxxxxxxxx
---
 drivers/iio/adc/stm32-adc.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
index 5c6c06b269be..b77f39f305d8 100644
--- a/drivers/iio/adc/stm32-adc.c
+++ b/drivers/iio/adc/stm32-adc.c
@@ -2263,33 +2263,37 @@ static int stm32_adc_populate_int_ch(struct iio_dev *indio_dev, const char *ch_n
 
 	for (i = 0; i < STM32_ADC_INT_CH_NB; i++) {
 		if (!strncmp(stm32_adc_ic[i].name, ch_name, STM32_ADC_CH_SZ)) {
+			bool na;
+
 			/* Check internal channel availability */
 			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);
+				na = !adc->cfg->regs->or_vddcore.reg;
 				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);
+				na = !adc->cfg->regs->or_vddcpu.reg;
 				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);
+				na = !adc->cfg->regs->or_vddq_ddr.reg;
 				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);
+				na = !adc->cfg->regs->ccr_vref.reg;
 				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);
+				na = !adc->cfg->regs->ccr_vbat.reg;
 				break;
+			default:
+				return -EINVAL;
+			}
+
+			if (na) {
+				/*
+				 * Channel label matches an internal STM32 ADC channel.
+				 * Warn about it, as there's normally no restriction on the
+				 * name but that's not among available 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) {

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

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