arch: arm: core: aarch32: support for On-Chip Memory (OCM) areas in aarch32

Introduce support for On-Chip Memory (OCM) areas in aarch32 Cortex-A
SoCs. This memory area is suitable for, amongst other things, un-
cached device DMA. The OCM memory can reside either at address zero
or at a high memory address, with configuration of the memory's lo-
cation similar to the configuration of the location of the exception
vectors. In both cases, it must be assured that the low/high OCM
area declaration doesn't overlap with the exception vectors memory
page at either the low/high address. Therefore, all possible OCM
location options shall be described in the SoC's device tree, the
current location shall be indicated via a "chosen" entry in the
target board's device tree.

This commit contains the necessary changes to the linker-related
files as well as the static region declaration for the MMU in-
itialization in the Zynq-7000 SoC-specific init code.

Signed-off-by: Immo Birnbaum <Immo.Birnbaum@weidmueller.com>

include/arch/arm/aarch32/cortex_a_r/scripts/linker.ld

@@ -15,6 +15,7 @@
 #include <linker/sections.h>
 #include <devicetree.h>
 
+#include <linker/devicetree_regions.h>
 #include <linker/linker-defs.h>
 #include <linker/linker-tool.h>
 
@@ -80,6 +81,7 @@ MEMORY
 {
     FLASH    (rx) : ORIGIN = ROM_ADDR, LENGTH = ROM_SIZE
     SRAM     (wx) : ORIGIN = RAM_ADDR, LENGTH = RAM_SIZE
+    LINKER_DT_REGION_FROM_NODE(OCM, rw, DT_CHOSEN(zephyr_ocm))
     /* Used by and documented in include/linker/intlist.ld */
     IDT_LIST (wx) : ORIGIN = 0xFFFFF7FF, LENGTH = 2K
 }
@@ -340,6 +342,32 @@ SECTIONS
 
     GROUP_END(RAMABLE_REGION)
 
+#if DT_NODE_HAS_STATUS(DT_CHOSEN(zephyr_ocm), okay)
+GROUP_START(OCM)
+
+	SECTION_PROLOGUE(_OCM_BSS_SECTION_NAME, (NOLOAD),SUBALIGN(4))
+	{
+		__ocm_start = .;
+		__ocm_bss_start = .;
+		*(.ocm_bss)
+		*(".ocm_bss.*")
+		__ocm_bss_end = .;
+	} GROUP_LINK_IN(OCM)
+
+	SECTION_PROLOGUE(_OCM_DATA_SECTION_NAME,,SUBALIGN(4))
+	{
+		__ocm_data_start = .;
+		*(.ocm_data)
+		*(".ocm_data.*")
+		__ocm_data_end = .;
+	} GROUP_LINK_IN(OCM)
+
+  __ocm_end = .;
+  __ocm_size = __ocm_end - __ocm_start;
+
+GROUP_END(OCM)
+#endif
+
 /* Located in generated directory. This file is populated by the
  * zephyr_linker_sources() Cmake function.
  */

include/linker/linker-defs.h

@@ -306,6 +306,12 @@ extern char __dtcm_start[];
 extern char __dtcm_end[];
 #endif
 
+#if DT_NODE_HAS_STATUS(DT_CHOSEN(zephyr_ocm), okay)
+extern char __ocm_start[];
+extern char __ocm_end[];
+extern char __ocm_size[];
+#endif
+
 /* Used by the Security Attribution Unit to configure the
  * Non-Secure Callable region.
  */

include/linker/section_tags.h

@@ -28,6 +28,8 @@
 #define __dtcm_data_section Z_GENERIC_SECTION(_DTCM_DATA_SECTION_NAME)
 #define __dtcm_bss_section Z_GENERIC_SECTION(_DTCM_BSS_SECTION_NAME)
 #define __dtcm_noinit_section Z_GENERIC_SECTION(_DTCM_NOINIT_SECTION_NAME)
+#define __ocm_data_section Z_GENERIC_SECTION(_OCM_DATA_SECTION_NAME)
+#define __ocm_bss_section Z_GENERIC_SECTION(_OCM_BSS_SECTION_NAME)
 #define __imx_boot_conf_section Z_GENERIC_SECTION(_IMX_BOOT_CONF_SECTION_NAME)
 #define __imx_boot_data_section Z_GENERIC_SECTION(_IMX_BOOT_DATA_SECTION_NAME)
 #define __imx_boot_ivt_section Z_GENERIC_SECTION(_IMX_BOOT_IVT_SECTION_NAME)

include/linker/sections.h

@@ -42,7 +42,7 @@
 /* Architecture-specific sections */
 #if defined(CONFIG_ARM)
 #define _KINETIS_FLASH_CONFIG_SECTION_NAME  kinetis_flash_config
-#define _TI_CCFG_SECTION_NAME	.ti_ccfg
+#define _TI_CCFG_SECTION_NAME	        .ti_ccfg
 
 #define _CCM_DATA_SECTION_NAME		.ccm_data
 #define _CCM_BSS_SECTION_NAME		.ccm_bss
@@ -50,9 +50,12 @@
 
 #define _ITCM_SECTION_NAME		.itcm
 
-#define _DTCM_DATA_SECTION_NAME	.dtcm_data
+#define _DTCM_DATA_SECTION_NAME	        .dtcm_data
 #define _DTCM_BSS_SECTION_NAME		.dtcm_bss
 #define _DTCM_NOINIT_SECTION_NAME	.dtcm_noinit
+
+#define _OCM_DATA_SECTION_NAME	        .ocm_data
+#define _OCM_BSS_SECTION_NAME		.ocm_bss
 #endif
 
 #define _IMX_BOOT_CONF_SECTION_NAME	.boot_hdr.conf