arch: arm: mpu: allow optional region gap filling in the ARMv8-M MPU

We allow the run-time, full paritioning of the SRAM space by the
ARMv8-M MPU driver to be an optional feature.

Signed-off-by: Ioannis Glaropoulos <[email protected]>

Author: ioannisg

arch/arm/core/cortex_m/mpu/arm_core_mpu_dev.h

@@ -29,7 +29,7 @@ struct k_thread;
  * @param mpu_regions_num the number of available HW MPU regions.
  */
 #if defined(CONFIG_MPU_REQUIRES_NON_OVERLAPPING_REGIONS) && \
-	!defined(CONFIG_MPU_SKIP_BACKGROUND_SRAM_FILLING)
+	defined(CONFIG_MPU_GAP_FILLING)
 /*
  * For ARM MPU architectures, where the domain partitions cannot be defined
  * on top of the statically configured memory regions, the maximum number of
@@ -55,7 +55,7 @@ struct k_thread;
  *        memory region for (user) Thread Stack.
  */
 #if defined(CONFIG_MPU_REQUIRES_NON_OVERLAPPING_REGIONS) && \
-	!defined(CONFIG_MPU_SKIP_BACKGROUND_SRAM_FILLING)
+	defined(CONFIG_MPU_GAP_FILLING)
 /* When dynamic regions may not be defined on top of statically
  * allocated memory regions, defining a region for a thread stack
  * requires two additional MPU regions to be configured; one for
@@ -76,7 +76,7 @@ struct k_thread;
  *        memory region for a (supervisor) Thread Stack Guard.
  */
 #if (defined(CONFIG_MPU_REQUIRES_NON_OVERLAPPING_REGIONS) && \
-		!defined(CONFIG_MPU_SKIP_BACKGROUND_SRAM_FILLING)) \
+		defined(CONFIG_MPU_GAP_FILLING)) \
 	|| defined(CONFIG_CPU_HAS_NXP_MPU)
 /*
  * When dynamic regions may not be defined on top of statically

arch/arm/core/cortex_m/mpu/arm_mpu.c

@@ -101,7 +101,7 @@ static int mpu_configure_region(const u8_t index,
 }
 
 #if !defined(CONFIG_MPU_REQUIRES_NON_OVERLAPPING_REGIONS) || \
-	!defined(CONFIG_MPU_SRAM_GAP_FILLING)
+	!defined(CONFIG_MPU_GAP_FILLING)
 /* This internal function programs a set of given MPU regions
  * over a background memory area, optionally performing a
  * sanity check of the memory regions to be programmed.

arch/arm/core/cortex_m/mpu/arm_mpu_v8_internal.h

@@ -318,11 +318,20 @@ static int region_allocate_and_init(const u8_t index,
 static int mpu_configure_region(const u8_t index,
 	const struct k_mem_partition *new_region);
 
+#if !defined(CONFIG_MPU_GAP_FILLING)
+static int mpu_configure_regions(const struct k_mem_partition
+	*regions[], u8_t regions_num, u8_t start_reg_index,
+	bool do_sanity_check);
+#endif
+
 /* This internal function programs a set of given MPU regions
  * over a background memory area, optionally performing a
  * sanity check of the memory regions to be programmed.
+ *
+ * The function performs a full partition of the background memory
+ * area, effectively, leaving no space in this area uncovered by MPU.
  */
-static int mpu_configure_regions(const struct k_mem_partition
+static int mpu_configure_regions_and_partition(const struct k_mem_partition
 	*regions[], u8_t regions_num, u8_t start_reg_index,
 	bool do_sanity_check)
 {
@@ -472,7 +481,7 @@ static int mpu_configure_static_mpu_regions(const struct k_mem_partition
 	ARG_UNUSED(background_area_base);
 	ARG_UNUSED(background_area_end);
 
-	mpu_reg_index = mpu_configure_regions(static_regions,
+	mpu_reg_index = mpu_configure_regions_and_partition(static_regions,
 		regions_num, mpu_reg_index, true);
 
 	static_regions_num = mpu_reg_index;
@@ -539,6 +548,7 @@ static int mpu_configure_dynamic_mpu_regions(const struct k_mem_partition
 		ARM_MPU_ClrRegion(i);
 	}
 
+#if defined(CONFIG_MPU_GAP_FILLING)
 	/* Reset MPU regions inside which dynamic memory regions may
 	 * be programmed.
 	 */
@@ -551,10 +561,25 @@ static int mpu_configure_dynamic_mpu_regions(const struct k_mem_partition
 	 * forming a full partition of the background area, specified by the
 	 * given boundaries.
 	 */
+	mpu_reg_index = mpu_configure_regions_and_partition(dynamic_regions,
+		regions_num, mpu_reg_index, true);
+#else
+
+	/* We are going to skip the full partition of the background areas.
+	 * So we can disable MPU regions inside which dynamic memroy regions
+	 * may be programmed.
+	 */
+	for (int i = 0; i < MPU_DYNAMIC_REGION_AREAS_NUM; i++) {
+		ARM_MPU_ClrRegion(dyn_reg_info[i].index);
+	}
 
+	/* The dynamic regions are now programmed on top of
+	 * existing SRAM region configuration.
+	 */
 	mpu_reg_index = mpu_configure_regions(dynamic_regions,
 		regions_num, mpu_reg_index, true);
 
+#endif /* CONFIG_MPU_GAP_FILLING */
 	return mpu_reg_index;
 }