mainboard/qemu-aarch64: Get top of memory from device-tree blob

Trying to probe RAM space to figure out top of memory causes an
exception on AArch64 virtual machines with recent versions of QEMU, but
we temporarily enable exception handlers for that and use it to help
detect if a RAM address is usable or not. However, QEMU docs recommend
reading device information from the device-tree blob it provides us at
the start of RAM.

A previous commit adds a library function to parse device-tree blob that
QEMU provides us. Use it to determine top of memory in AArch64 QEMU
virtual machines, but still fall back to the RAM probing approach as a
last-ditch effort.

Change-Id: I4cc888b57cf98e0797ce7f9ddfa2eb34d14cd9c1
Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80364
Reviewed-by: Maximilian Brune <maximilian.brune@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/mainboard/emulation/qemu-aarch64/Kconfig

@@ -11,6 +11,7 @@ config BOARD_SPECIFIC_OPTIONS
 	select ARCH_VERSTAGE_ARMV8_64
 	select ARCH_ROMSTAGE_ARMV8_64
 	select ARCH_RAMSTAGE_ARMV8_64
+	select FLATTENED_DEVICE_TREE
 	select ARM64_USE_ARCH_TIMER
 	select BOARD_ROMSIZE_KB_16384
 	select BOOTBLOCK_CUSTOM

src/mainboard/emulation/qemu-aarch64/cbmem.c

@@ -3,8 +3,16 @@
 #include <cbmem.h>
 #include <ramdetect.h>
 #include <symbols.h>
+#include <device_tree.h>
 
+DECLARE_REGION(fdt)
 uintptr_t cbmem_top_chipset(void)
 {
+	uint64_t top;
+
+	top = fdt_get_memory_top((void *)_fdt);
+	if (top)
+		return MIN(top, (uint64_t)4 * GiB - 1);
+
 	return (uintptr_t)_dram + (probe_ramsize((uintptr_t)_dram, CONFIG_DRAM_SIZE_MB) * MiB);
 }

src/mainboard/emulation/qemu-aarch64/memlayout.ld

@@ -18,6 +18,7 @@ SECTIONS
 
 	BL31(0xe000000, 0x1000000)
 	DRAM_START(0x40000000)
+	REGION(fdt, 0x40000000, 1M, 8)
 	BOOTBLOCK(0x60010000, 64K)
 	STACK(0x60020000, 54K)
 	CBFS_MCACHE(0x6002D800, 8K)