mach-stm32: Use default memory map as background region

On linux kernel side, on STM32F7 and STM32H7 SoCs, DMA requires
uncachable regions. These regions are defined in DT.
Since kernel linux v4.15, on ARMv7-M Cortex, kernel is able
to configure MPU regions depending on DT settings.

As kernel is able to configure MPU, this allows to remove
MPU region settings in bootloader.

On Cortex M processors, MPU allows to use a default memory map.
(see B3.5.4 MPU Control Register, MPU_CTRL in
https://developer.arm.com/products/architecture/m-profile/docs/ddi0403/latest/armv7-m-architecture-reference-manual)
Use the default memory map as background region for all STM32 SoCs
family with an additional MPU region corresponding to the SDRAM area.
Signed-off-by: NPatrice Chotard <patrice.chotard@st.com>

arch/arm/cpu/armv7m/mpu.c

@@ -10,12 +10,13 @@
 #include <asm/armv7m_mpu.h>
 #include <asm/io.h>
 
-#define V7M_MPU_CTRL_ENABLE		(1 << 0)
+#define V7M_MPU_CTRL_ENABLE		BIT(0)
 #define V7M_MPU_CTRL_DISABLE		(0 << 0)
-#define V7M_MPU_CTRL_HFNMIENA		(1 << 1)
-#define VALID_REGION			(1 << 4)
+#define V7M_MPU_CTRL_HFNMIENA		BIT(1)
+#define V7M_MPU_CTRL_PRIVDEFENA		BIT(2)
+#define VALID_REGION			BIT(4)
 
-#define ENABLE_REGION			(1 << 0)
+#define ENABLE_REGION			BIT(0)
 
 #define AP_SHIFT			24
 #define XN_SHIFT			28
@@ -36,7 +37,7 @@ void disable_mpu(void)
 
 void enable_mpu(void)
 {
-	writel(V7M_MPU_CTRL_ENABLE | V7M_MPU_CTRL_HFNMIENA, &V7M_MPU->ctrl);
+	writel(V7M_MPU_CTRL_ENABLE | V7M_MPU_CTRL_PRIVDEFENA, &V7M_MPU->ctrl);
 
 	/* Make sure new mpu config is effective for next memory access */
 	dsb();

arch/arm/mach-stm32/soc.c

@@ -15,35 +15,21 @@ int arch_cpu_init(void)
 
 	struct mpu_region_config stm32_region_config[] = {
 		/*
-		 * Make all 4GB cacheable & executable. We are overriding it
-		 * with next region for any requirement. e.g. below region1,
-		 * 2 etc.
-		 * In other words, the area not coming in following
-		 * regions configuration is the one configured here in region_0
-		 * (cacheable & executable).
+		 * Make SDRAM area cacheable & executable.
 		 */
+#if defined(CONFIG_STM32F4)
 		{ 0x00000000, REGION_0, XN_DIS, PRIV_RW_USR_RW,
-		O_I_WB_RD_WR_ALLOC, REGION_4GB },
-
-		/* armv7m code area */
-		{ 0x00000000, REGION_1, XN_DIS, PRIV_RW_USR_RW,
-		STRONG_ORDER, REGION_512MB },
-
-		/* Device area : Not executable */
-		{ 0x40000000, REGION_2, XN_EN, PRIV_RW_USR_RW,
-		DEVICE_NON_SHARED, REGION_512MB },
+		O_I_WB_RD_WR_ALLOC, REGION_16MB },
+#endif
 
-		/*
-		 * Armv7m fixed configuration: strongly ordered & not
-		 * executable, not cacheable
-		 */
-		{ 0xE0000000, REGION_3, XN_EN, PRIV_RW_USR_RW,
-		STRONG_ORDER, REGION_512MB },
+#if defined(CONFIG_STM32F7)
+		{ 0xC0000000, REGION_0, XN_DIS, PRIV_RW_USR_RW,
+		O_I_WB_RD_WR_ALLOC, REGION_16MB },
+#endif
 
-#if !defined(CONFIG_STM32H7)
-		/* Device area : Not executable */
-		{ 0xA0000000, REGION_4, XN_EN, PRIV_RW_USR_RW,
-		DEVICE_NON_SHARED, REGION_512MB },
+#if defined(CONFIG_STM32H7)
+		{ 0xD0000000, REGION_0, XN_DIS, PRIV_RW_USR_RW,
+		O_I_WB_RD_WR_ALLOC, REGION_32MB },
 #endif
 	};