lib: open-amp: support resource table relocation

There are some remote processing scenarios where the resource table needs
to be moved to another location. This can be either because there is no
way to exchange the location of the resource table between the two
processors and they have to agree on a fixed predefined location, or
because the memory segment where the current resource table resides is not
is accessible/writable by the remote processor.
A real example of such a case can be found in the Linux rproc driver for
i.MX SoCs. A memory area containing the resource table can be specified
there in the device tree. Since this feature is application dependent, it
can optionally be configured in the device tree along with the other
open-amp related nodes.

This device tree snippet is intended to illustrate a possible use case:
[..]
chosen {
    zephyr,ipc_shm = &ipc_shm;
    zephyr,rsc_table = &rsc_table;
    zephyr,ipc = &mailbox0;
};

reserved-memory {
    #address-cells = <1>;
    #size-cells = <1>;
    ranges;

    ipc_shm: memory@55000000 {
        reg = <0x55000000 0x500000>;
    };

    rsc_table: rsc-table@550ff000 {
        reg = <0x550ff000 0x1000>;
    };
};
[..]

Signed-off-by: Matthias Fend <[email protected]>

Author: emfend

doc/build/dts/api/api.rst

@@ -421,6 +421,9 @@ device.
      - Used by the OpenThread to specify UART device for Spinel protocol
    * - zephyr,pcie-controller
      - The node corresponding to the PCIe Controller
+   * - zephyr,rsc_table
+     - The resource table is copied to the "reserved memory" area specified
+       by the ``zephyr,rsc_table`` node
    * - zephyr,settings-partition
      - Fixed partition node. If defined this selects the partition used
        by the NVS and FCB settings backends.

lib/open-amp/resource_table.c

@@ -72,8 +72,33 @@ static struct fw_resource_table __resource resource_table = {
 #endif
 };
 
+#if DT_HAS_CHOSEN(zephyr_rsc_table)
+
+#define RSC_TABLE_RELOC			DT_CHOSEN(zephyr_rsc_table)
+#define RSC_TABLE_RELOC_START		DT_REG_ADDR(RSC_TABLE_RELOC)
+#define RSC_TABLE_RELOC_SIZE		DT_REG_SIZE(RSC_TABLE_RELOC)
+
+BUILD_ASSERT(sizeof(resource_table) <= RSC_TABLE_RELOC_SIZE,
+	     "Resource table does not fit in the relocation area");
+
+#endif
+
 void rsc_table_get(void **table_ptr, int *length)
 {
+#if defined(RSC_TABLE_RELOC)
+	const size_t cmp_size = offsetof(struct fw_resource_table, offset) + sizeof(((struct fw_resource_table *)0)->offset);
+
+	*table_ptr = (void *)RSC_TABLE_RELOC_START;
+	*length = sizeof(resource_table);
+
+	/*
+	 * Do not copy the resource table if it has already been installed from the remote host.
+	 * Because the remote host may have already initialized some fields, only the guaranteed constant bytes can be compared.
+	 */
+	if(memcmp(&resource_table, *table_ptr, cmp_size))
+		memcpy(*table_ptr, (void *)&resource_table, *length);
+#else
 	*table_ptr = (void *)&resource_table;
 	*length = sizeof(resource_table);
+#endif
 }