arm64: mvebu: Restrict memory size to a usable maximum

Not all memory is mapped in the MMU. So we need to restrict the memory
size so that U-Boot does not try to access it. Also, the internal
registers are located at 0xf000.0000 - 0xffff.ffff. Currently only 2GiB
are mapped for system memory. This is what we pass to the U-Boot
subsystem here.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Nadav Haklai <nadavh@marvell.com>
Cc: Neta Zur Hershkovits <neta@marvell.com>
Cc: Kostya Porotchkin <kostap@marvell.com>
Cc: Omri Itach <omrii@marvell.com>
Cc: Igal Liberman <igall@marvell.com>
Cc: Haim Boot <hayim@marvell.com>
Cc: Hanna Hawa <hannah@marvell.com>

arch/arm/mach-mvebu/arm64-common.c

@@ -16,6 +16,23 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
+/*
+ * Not all memory is mapped in the MMU. So we need to restrict the
+ * memory size so that U-Boot does not try to access it. Also, the
+ * internal registers are located at 0xf000.0000 - 0xffff.ffff.
+ * Currently only 2GiB are mapped for system memory. This is what
+ * we pass to the U-Boot subsystem here.
+ */
+#define USABLE_RAM_SIZE		0x80000000
+
+ulong board_get_usable_ram_top(ulong total_size)
+{
+	if (gd->ram_size > USABLE_RAM_SIZE)
+		return USABLE_RAM_SIZE;
+
+	return gd->ram_size;
+}
+
 /*
  * On ARMv8, MBus is not configured in U-Boot. To enable compilation
  * of the already implemented drivers, lets add a dummy version of