From 46e3b96dd800d2d4f2e6cf4118eb40b5ab65cfab Mon Sep 17 00:00:00 2001
From: Johan Lafon <johan.lafon@syslinbit.com>
Date: Thu, 14 Nov 2024 12:23:13 +0100
Subject: [PATCH] drivers: adc: fix mV conversion error with high resolution
 ADC data

Fix the overflow encountered with too high resolution ADC output data
when using adc_raw_to_millivolts. This is done by using int64_t instead
of a int32_t for the internal computations.

Signed-off-by: Johan Lafon <johan.lafon@syslinbit.com>
---
 drivers/adc/adc_common.c     | 2 +-
 drivers/adc/adc_emul.c       | 2 +-
 include/zephyr/drivers/adc.h | 6 +++---
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/adc/adc_common.c b/drivers/adc/adc_common.c
index cf6472718dec0..aa25ed7a4643e 100644
--- a/drivers/adc/adc_common.c
+++ b/drivers/adc/adc_common.c
@@ -7,7 +7,7 @@
 #include <zephyr/drivers/adc.h>
 
 int adc_gain_invert(enum adc_gain gain,
-		    int32_t *value)
+		    int64_t *value)
 {
 	struct gain_desc {
 		uint8_t mul;
diff --git a/drivers/adc/adc_emul.c b/drivers/adc/adc_emul.c
index 20b9764fd5fbb..759af792b0efb 100644
--- a/drivers/adc/adc_emul.c
+++ b/drivers/adc/adc_emul.c
@@ -406,7 +406,7 @@ static int adc_emul_get_chan_value(struct adc_emul_data *data,
 {
 	struct adc_emul_chan_cfg *chan_cfg = &data->chan_cfg[chan];
 	uint32_t input_mV;
-	uint32_t ref_v;
+	uint64_t ref_v;
 	uint64_t temp; /* Temporary 64 bit value prevent overflows */
 	int err = 0;
 
diff --git a/include/zephyr/drivers/adc.h b/include/zephyr/drivers/adc.h
index 583c04cd0e71e..0689929cc8e8e 100644
--- a/include/zephyr/drivers/adc.h
+++ b/include/zephyr/drivers/adc.h
@@ -71,7 +71,7 @@ enum adc_gain {
  * @retval -EINVAL if the gain could not be interpreted
  */
 int adc_gain_invert(enum adc_gain gain,
-		    int32_t *value);
+		    int64_t *value);
 
 /** @brief ADC references. */
 enum adc_reference {
@@ -880,11 +880,11 @@ static inline int adc_raw_to_millivolts(int32_t ref_mv,
 					uint8_t resolution,
 					int32_t *valp)
 {
-	int32_t adc_mv = *valp * ref_mv;
+	int64_t adc_mv = ((uint64_t) *valp) * ref_mv;
 	int ret = adc_gain_invert(gain, &adc_mv);
 
 	if (ret == 0) {
-		*valp = (adc_mv >> resolution);
+		*valp = (uint32_t) (adc_mv >> resolution);
 	}
 
 	return ret;