driver: flash: stm32 rdp option byte reloaded with power on reset

for the read-back protection option byte to be successfully reloaded at
runtime, a power-on reset can be achieved by putting the microcontroller
into Standby mode and waking up from that mode.

Signed-off-by: Cyril Fougeray <[email protected]>

Author: fouge

drivers/flash/flash_stm32g4x.c

@@ -17,6 +17,8 @@ LOG_MODULE_REGISTER(LOG_DOMAIN);
 #include <zephyr/init.h>
 #include <soc.h>
 #include <stm32_ll_system.h>
+#include <stm32g4xx_ll_cortex.h>
+#include <stm32g4xx_ll_pwr.h>
 
 #include "flash_stm32.h"
 
@@ -318,6 +320,15 @@ void flash_stm32_set_rdp_level(const struct device *dev, uint8_t level)
 {
 	flash_stm32_option_bytes_write(dev, FLASH_OPTR_RDP_Msk,
 				       (uint32_t)level << FLASH_OPTR_RDP_Pos);
+
+	/*
+	 * POR needed to reload option bytes, done at runtime by entering standby mode
+	 * /!\ make sure a wakeup source is configured!
+	 */
+	LL_PWR_SetPowerMode(LL_PWR_MODE_STANDBY);
+	LL_LPM_EnableDeepSleep();
+	/* enter SLEEP mode : WFE or WFI */
+	k_cpu_idle();
 }
 #endif /* CONFIG_FLASH_STM32_READOUT_PROTECTION */
 

drivers/flash/flash_stm32l4x.c

@@ -18,6 +18,8 @@ LOG_MODULE_REGISTER(LOG_DOMAIN);
 #include <zephyr/sys/barrier.h>
 #include <zephyr/init.h>
 #include <soc.h>
+#include <stm32l4xx_ll_cortex.h>
+#include <stm32l4xx_ll_pwr.h>
 
 #include "flash_stm32.h"
 
@@ -309,6 +311,15 @@ void flash_stm32_set_rdp_level(const struct device *dev, uint8_t level)
 {
 	flash_stm32_option_bytes_write(dev, FLASH_OPTR_RDP_Msk,
 				       (uint32_t)level << FLASH_OPTR_RDP_Pos);
+
+	/*
+	 * POR needed to reload option bytes, done at runtime by entering standby mode
+	 * /!\ make sure a wakeup source is configured!
+	 */
+	LL_PWR_SetPowerMode(LL_PWR_MODE_STANDBY);
+	LL_LPM_EnableDeepSleep();
+	/* enter SLEEP mode : WFE or WFI */
+	k_cpu_idle();
 }
 #endif /* CONFIG_FLASH_STM32_READOUT_PROTECTION */