drivers/adc: stm32: workaround for L462xE errata 2.5.2 and stuck reads

According to the ST Errata sheet ES0389 - Rev 5, section 2.5.2, the
workaround to the issue of "Wrong ADC result if conversion done late
after calibration or previous conversion" is to perform two consecutive
ADC conversions.
We found also that the same objective is achieved enabling and disabling
it at every read. Moreover, this approach solves another issue found on
several STM32L462VE samples, where the reads were stuck, giving always
the same wrong value, that was 0 or the last calibration value.

Additional clearing of ADRDY flag has been added to avoid finding it
already set before next enabling.

Signed-off-by: Giancarlo Stasi <[email protected]>

Author: giansta

drivers/adc/adc_stm32.c

@@ -502,15 +502,61 @@ static void adc_stm32_isr(const struct device *dev)
 	LOG_DBG("ISR triggered.");
 }
 
+static int adc_stm32_enable_and_wait_stabilisation(ADC_TypeDef *adc)
+{
+#if defined(CONFIG_SOC_SERIES_STM32L4X) || \
+	defined(CONFIG_SOC_SERIES_STM32L5X) || \
+	defined(CONFIG_SOC_SERIES_STM32WBX) || \
+	defined(CONFIG_SOC_SERIES_STM32G0X) || \
+	defined(CONFIG_SOC_SERIES_STM32G4X) || \
+	defined(CONFIG_SOC_SERIES_STM32H7X) || \
+	defined(CONFIG_SOC_SERIES_STM32WLX)
+	/*
+	 * Enabling ADC modules in L4, WB, G0 and G4 series may fail if they are
+	 * still not stabilized, this will wait for a short time to ensure ADC
+	 * modules are properly enabled.
+	 */
+	uint32_t countTimeout = 0;
+
+	do {
+		if (LL_ADC_IsEnabled(adc) == 0UL) {
+			LL_ADC_Enable(adc);
+		}
+		countTimeout++;
+		if (countTimeout == 10) {
+			return -ETIMEDOUT;
+		}
+	} while (LL_ADC_IsActiveFlag_ADRDY(adc) == 0);
+	LL_ADC_ClearFlag_ADRDY(adc);
+#else
+	if (LL_ADC_IsEnabled(adc) == 0UL) {
+		LL_ADC_Enable(adc);
+	}
+#endif
+	return 0;
+}
+
 static int adc_stm32_read(const struct device *dev,
 			  const struct adc_sequence *sequence)
 {
 	struct adc_stm32_data *data = dev->data;
-	int error;
+	const struct adc_stm32_cfg *config = dev->config;
+	ADC_TypeDef *adc = (ADC_TypeDef *)config->base;
+	int error = 0;
 
-	adc_context_lock(&data->ctx, false, NULL);
-	error = start_read(dev, sequence);
-	adc_context_release(&data->ctx, error);
+	if (LL_ADC_IsEnabled(adc) == 0) {
+		error = adc_stm32_enable_and_wait_stabilisation(adc);
+	}
+
+	if (error == 0) {
+		adc_context_lock(&data->ctx, false, NULL);
+		error = start_read(dev, sequence);
+		adc_context_release(&data->ctx, error);
+	}
+
+	if (LL_ADC_IsEnabled(adc)) {
+		LL_ADC_Disable(adc);
+	}
 
 	return error;
 }
@@ -796,32 +842,10 @@ static int adc_stm32_init(const struct device *dev)
 	}
 #endif
 
-	LL_ADC_Enable(adc);
-
-#if defined(CONFIG_SOC_SERIES_STM32L4X) || \
-	defined(CONFIG_SOC_SERIES_STM32L5X) || \
-	defined(CONFIG_SOC_SERIES_STM32WBX) || \
-	defined(CONFIG_SOC_SERIES_STM32G0X) || \
-	defined(CONFIG_SOC_SERIES_STM32G4X) || \
-	defined(CONFIG_SOC_SERIES_STM32H7X) || \
-	defined(CONFIG_SOC_SERIES_STM32WLX)
-	/*
-	 * Enabling ADC modules in L4, WB, G0 and G4 series may fail if they are
-	 * still not stabilized, this will wait for a short time to ensure ADC
-	 * modules are properly enabled.
-	 */
-	uint32_t countTimeout = 0;
-
-	while (LL_ADC_IsActiveFlag_ADRDY(adc) == 0) {
-		if (LL_ADC_IsEnabled(adc) == 0UL) {
-			LL_ADC_Enable(adc);
-			countTimeout++;
-			if (countTimeout == 10) {
-				return -ETIMEDOUT;
-			}
-		}
+	err = adc_stm32_enable_and_wait_stabilisation(adc);
+	if (err < 0) {
+		return err;
 	}
-#endif
 
 	config->irq_cfg_func();