drivers: flash: Add support for defining custom RDP1 byte value

This patch makes possible to choose custom byte which should be used
to enable non-permanent readout protection (RDP1). Actually, any byte
except 0xAA and 0xCC (which are used by RDP0 and RDP2 respectively)
can be used to enable RDP1 but in multi-image environment, some other
image could check if RDP1 is enabled by comparing it to some hardcoded
value.

If property is not defined, 0x55 will be used to enable RDP1. The
default value comes from STM32 HAL.

Signed-off-by: Patryk Duda <[email protected]>

Author: duda-patryk

drivers/flash/flash_stm32.h

@@ -226,8 +226,13 @@ struct flash_stm32_priv {
 				FLASH_STM32_SR_PGPERR)
 
 #define FLASH_STM32_RDP0 0xAA
-#define FLASH_STM32_RDP1 0x55
 #define FLASH_STM32_RDP2 0xCC
+#define FLASH_STM32_RDP1                                                       \
+	DT_PROP(DT_INST(0, st_stm32_flash_controller), st_rdp1_enable_byte)
+
+#if FLASH_STM32_RDP1 == FLASH_STM32_RDP0 || FLASH_STM32_RDP1 == FLASH_STM32_RDP2
+#error RDP1 byte has to be different than RDP0 and RDP2 byte
+#endif
 
 #ifdef CONFIG_FLASH_PAGE_LAYOUT
 static inline bool flash_stm32_range_exists(const struct device *dev,

dts/bindings/flash_controller/st,stm32-flash-controller.yaml

@@ -3,3 +3,15 @@ description: STM32 Family flash controller
 compatible: "st,stm32-flash-controller"
 
 include: flash-controller.yaml
+
+properties:
+  st,rdp1-enable-byte:
+    type: int
+    default: 0x55
+    description: |
+      This property provides a byte which should used to enable non-permanent
+      readout protection (RDP1). Actually, any byte except 0xAA and 0xCC
+      (which are used by RDP0 and RDP2 respectively) can be used to enable
+      RDP1 but in multi-image environment, some other image could check if
+      RDP1 is enabled by comparing it to some hardcoded value. The byte has to
+      be different than 0xAA and 0xCC.