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

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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>
This commit is contained in:
Stephen Warren 2018-08-30 15:43:44 -06:00 committed by Alexander Graf
parent 9b5e6396bf
commit 0797f7f0b7
1 changed files with 14 additions and 0 deletions
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14
arch/arm/mach-tegra/board2.c
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@ -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");