arch: common: Make nocache region loadable

The `nocache` is not loadable, thus data stored therein cannot be
initialized by the startup code. This might be needed in special
cases. E.g. One might have a buffer which one wants to DMA into,
and which is a member of a struct. Other members of the struct one
may want to have initialized by the startup code.
The buffer thus should be placed in the `nocache` region, but for
the other members of the buffer to be initialized by the startup
code, the `nocache` region needs to be loadable.

Fix it by making the `nocache` region loadable. Adding a KConfig
symbol to do this optionally was considered, but deemed unnecessary
during the PR.

Signed-off-by: Julian Achatzi <mail@achatzi.pro>

arch/common/nocache.ld

@@ -8,7 +8,7 @@
 /* Copied from linker.ld */
 
 /* Non-cached region of RAM */
-SECTION_DATA_PROLOGUE(_NOCACHE_SECTION_NAME,(NOLOAD),)
+SECTION_DATA_PROLOGUE(_NOCACHE_SECTION_NAME,,)
 {
 #if defined(CONFIG_MMU)
 	MMU_ALIGN;
@@ -27,5 +27,6 @@ SECTION_DATA_PROLOGUE(_NOCACHE_SECTION_NAME,(NOLOAD),)
 	MPU_ALIGN(_nocache_ram_size);
 #endif
 	_nocache_ram_end = .;
-} GROUP_DATA_LINK_IN(RAMABLE_REGION, RAMABLE_REGION)
+} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
 _nocache_ram_size = _nocache_ram_end - _nocache_ram_start;
+_nocache_load_start = LOADADDR(_NOCACHE_SECTION_NAME);

include/zephyr/linker/linker-defs.h

@@ -225,6 +225,7 @@ extern char __sg_size[];
 extern char _nocache_ram_start[];
 extern char _nocache_ram_end[];
 extern char _nocache_ram_size[];
+extern char _nocache_load_start[];
 #endif /* CONFIG_NOCACHE_MEMORY */
 
 /* Memory owned by the kernel. Start and end will be aligned for memory

kernel/xip.c

@@ -31,6 +31,12 @@ void z_data_copy(void)
 	z_early_memcpy(&__ramfunc_region_start, &__ramfunc_load_start,
 		       __ramfunc_end - __ramfunc_region_start);
 #endif /* CONFIG_ARCH_HAS_RAMFUNC_SUPPORT */
+#ifdef CONFIG_ARCH_HAS_NOCACHE_MEMORY_SUPPORT
+#if CONFIG_NOCACHE_MEMORY
+	z_early_memcpy(&_nocache_ram_start, &_nocache_load_start,
+		       (uintptr_t) &_nocache_ram_size);
+#endif /* CONFIG_NOCACHE_MEMORY */
+#endif /* CONFIG_ARCH_HAS_NOCACHE_MEMORY_SUPPORT */
 #if DT_NODE_HAS_STATUS_OKAY(DT_CHOSEN(zephyr_ccm))
 	z_early_memcpy(&__ccm_data_start, &__ccm_data_load_start,
 		       __ccm_data_end - __ccm_data_start);