soc: atmel_sam0: The ADC reference is locked while enabled for SAML21

For SAML21-based parts, the REFCTRL register is locked while the ADC is
enabled. Permit some parts to declare that they need the ADC to be
disabled before modifying REFCTRL.

Signed-off-by: Attie Grande <[email protected]>

Author: attie-argentum

drivers/adc/adc_sam0.c

@@ -160,8 +160,16 @@ static int adc_sam0_channel_setup(const struct device *dev,
 		return -EINVAL;
 	}
 	if (adc->REFCTRL.reg != refctrl) {
+#ifdef ADC_SAM0_REFERENCE_ENABLE_PROTECTED
+		adc->CTRLA.bit.ENABLE = 0;
+		wait_synchronization(adc);
+#endif
 		adc->REFCTRL.reg = refctrl;
 		wait_synchronization(adc);
+#ifdef ADC_SAM0_REFERENCE_ENABLE_PROTECTED
+		adc->CTRLA.bit.ENABLE = 1;
+		wait_synchronization(adc);
+#endif
 #ifdef ADC_SAM0_REFERENCE_GLITCH
 		struct adc_sam0_data *data = dev->data;
 

soc/arm/atmel_sam0/saml21/soc.h

@@ -40,6 +40,8 @@
 
 #endif /* _ASMLANGUAGE */
 
+#define ADC_SAM0_REFERENCE_ENABLE_PROTECTED
+
 #include "adc_fixup_sam0.h"
 #include "../common/soc_port.h"
 #include "../common/atmel_sam0_dt.h"

soc/arm/atmel_sam0/samr34/soc.h

@@ -24,6 +24,8 @@
 
 #endif /* _ASMLANGUAGE */
 
+#define ADC_SAM0_REFERENCE_ENABLE_PROTECTED
+
 #include "adc_fixup_sam0.h"
 #include "../common/soc_port.h"
 #include "../common/atmel_sam0_dt.h"

soc/arm/atmel_sam0/samr35/soc.h

@@ -24,6 +24,8 @@
 
 #endif /* _ASMLANGUAGE */
 
+#define ADC_SAM0_REFERENCE_ENABLE_PROTECTED
+
 #include "adc_fixup_sam0.h"
 #include "../common/soc_port.h"
 #include "../common/atmel_sam0_dt.h"