ARM: tegra: reserve unmapped RAM so EFI doesn't use it

Tegra U-Boot ensures that board_get_usable_ram_top() never returns a value
over 4GB, since some peripherals can't access such addresses. However, on
systems with more than 2GB of RAM, RAM bank 1 does describe this extra
RAM, so that Linux (or whatever OS) can use it, subject to DMA
limitations. Since board_get_usable_ram_top() points at the top of RAM
bank 0, the memory locations describes by RAM bank 1 are not mapped by
U-Boot's MMU configuration, and so cannot be used for anything.

For some completely inexplicable reason, U-Boot's EFI support ignores the
value returned by board_get_usable_ram_top(), and EFI memory allocation
routines will return values above U-Boot's RAM top. This causes U-Boot to
crash when it accesses that RAM, since it isn't mapped by the MMU. One
use-case where this happens is TFTP download of a file on Jetson TX1
(p2371-2180).

This change explicitly tells the EFI code that this extra RAM should not
be used, thus avoiding the crash.

A previous attempt to make EFI honor board_get_usable_ram_top() was
rejected. So, this patch will need to be replicated for any board that
implements board_get_usable_ram_top().

Fixes: aa909462d0 ("efi_loader: efi_allocate_pages is too restrictive")
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/arm/mach-tegra/board2.c

@@ -6,6 +6,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <efi_loader.h>
 #include <errno.h>
 #include <ns16550.h>
 #include <usb.h>
@@ -210,6 +211,19 @@ int board_early_init_f(void)
 
 int board_late_init(void)
 {
+#if CONFIG_IS_ENABLED(EFI_LOADER)
+	if (gd->bd->bi_dram[1].start) {
+		/*
+		 * Only bank 0 is below board_get_usable_ram_top(), so all of
+		 * bank 1 is not mapped by the U-Boot MMU configuration, and so
+		 * we must prevent EFI from using it.
+		 */
+		efi_add_memory_map(gd->bd->bi_dram[1].start,
+				   gd->bd->bi_dram[1].size >> EFI_PAGE_SHIFT,
+				   EFI_BOOT_SERVICES_DATA, false);
+	}
+#endif
+
 #if defined(CONFIG_TEGRA_SUPPORT_NON_SECURE)
 	if (tegra_cpu_is_non_secure()) {
 		printf("CPU is in NS mode\n");