[nrf fromlist] drivers: adc: nrfx: enable negative values for single-ended ADC readings

Add custom nordic-specific ADC API to enable to read negative values
from a single-ended ADC channels.

Upstream PR #: 91704

Signed-off-by: Jakub Zymelka <[email protected]>

Author: jaz1-nordic

drivers/adc/adc_nrfx_saadc.c

@@ -110,6 +110,7 @@ struct driver_data {
 	bool enable_internal_timer;
 #endif
 	bool internal_timer_enabled;
+	bool correct_single_ended;
 };
 
 static struct driver_data m_data = {
@@ -121,6 +122,7 @@ static struct driver_data m_data = {
 	.enable_internal_timer = DT_INST_PROP(0, enable_internal_timer),
 #endif
 	.internal_timer_enabled = false,
+	.correct_single_ended = true,
 };
 
 /* Maximum value of the internal timer interval in microseconds. */
@@ -749,6 +751,20 @@ static int adc_nrfx_read(const struct device *dev,
 	int error;
 
 	adc_context_lock(&m_data.ctx, false, NULL);
+	m_data.correct_single_ended = true;
+	error = start_read(dev, sequence);
+	adc_context_release(&m_data.ctx, error);
+
+	return error;
+}
+
+int adc_nrf_read_single_ended_negative_results(const struct device *dev,
+					       const struct adc_sequence *sequence)
+{
+	int error;
+
+	adc_context_lock(&m_data.ctx, false, NULL);
+	m_data.correct_single_ended = false;
 	error = start_read(dev, sequence);
 	adc_context_release(&m_data.ctx, error);
 
@@ -764,6 +780,7 @@ static int adc_nrfx_read_async(const struct device *dev,
 	int error;
 
 	adc_context_lock(&m_data.ctx, true, async);
+	m_data.correct_single_ended = true;
 	error = start_read(dev, sequence);
 	adc_context_release(&m_data.ctx, error);
 
@@ -786,9 +803,11 @@ static void event_handler(const nrfx_saadc_evt_t *event)
 					   m_data.active_channel_cnt)),
 			event->data.done.p_buffer);
 
-		if (has_single_ended(&m_data.ctx.sequence)) {
-			correct_single_ended(&m_data.ctx.sequence, m_data.user_buffer,
-					     event->data.done.size);
+		if (m_data.correct_single_ended) {
+			if (has_single_ended(&m_data.ctx.sequence)) {
+				correct_single_ended(&m_data.ctx.sequence, m_data.user_buffer,
+						event->data.done.size);
+			}
 		}
 		adc_context_on_sampling_done(&m_data.ctx, DEVICE_DT_INST_GET(0));
 	} else if (event->type == NRFX_SAADC_EVT_CALIBRATEDONE) {

include/zephyr/drivers/adc/adc_nrf.h

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_DRIVERS_ADC_ADC_NRFX_H_
+#define ZEPHYR_INCLUDE_DRIVERS_ADC_ADC_NRFX_H_
+
+#include <zephyr/types.h>
+#include <zephyr/drivers/adc.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Set a read request.
+ *
+ * @param dev       Pointer to the device structure for the driver instance.
+ * @param sequence  Structure specifying requested sequence of samplings.
+ *
+ * The function works identically to adc_read(), but does not correct
+ * negative measurement results in single-ended mode.
+ *
+ * If invoked from user mode, any sequence struct options for callback must
+ * be NULL.
+ *
+ * @retval 0        On success.
+ * @retval -EINVAL  If a parameter with an invalid value has been provided.
+ * @retval -ENOMEM  If the provided buffer is too small to hold the results
+ *                  of all requested samplings.
+ * @retval -ENOTSUP If the requested mode of operation is not supported.
+ * @retval -EBUSY   If another sampling was triggered while the previous one
+ *                  was still in progress. This may occur only when samplings
+ *                  are done with intervals, and it indicates that the selected
+ *                  interval was too small. All requested samples are written
+ *                  in the buffer, but at least some of them were taken with
+ *                  an extra delay compared to what was scheduled.
+ */
+int adc_nrf_read_single_ended_negative_results(const struct device *dev,
+					       const struct adc_sequence *sequence);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_INCLUDE_DRIVERS_ADC_ADC_NRFX_H_ */