ARM: tegra: support running in non-secure mode

When the CPU is in non-secure (NS) mode (when running U-Boot under a
secure monitor), certain actions cannot be taken, since they would need
to write to secure-only registers. One example is configuring the ARM
architectural timer's CNTFRQ register.

We could support this in one of two ways:
1) Compile twice, once for secure mode (in which case anything goes) and
   once for non-secure mode (in which case certain actions are disabled).
   This complicates things, since everyone needs to keep track of
   different U-Boot binaries for different situations.
2) Detect NS mode at run-time, and optionally skip any impossible actions.
   This has the advantage of a single U-Boot binary working in all cases.

(2) is not possible on ARM in general, since there's no architectural way
to detect secure-vs-non-secure. However, there is a Tegra-specific way to
detect this.

This patches uses that feature to detect secure vs. NS mode on Tegra, and
uses that to:

* Skip the ARM arch timer initialization.

* Set/clear an environment variable so that boot scripts can take
  different action depending on which mode the CPU is in. This might be
  something like:
  if CPU is secure:
    load secure monitor code into RAM.
    boot secure monitor.
    secure monitor will restart (a new copy of) U-Boot in NS mode.
  else:
    execute normal boot process

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/board/nvidia/common/board.c b/board/nvidia/common/board.c
index 80ef8fdcb23..018dddba155 100644
--- a/board/nvidia/common/board.c
+++ b/board/nvidia/common/board.c
@@ -21,6 +21,7 @@
 #include <asm/arch/pwm.h>
 #endif
 #include <asm/arch/tegra.h>
+#include <asm/arch-tegra/ap.h>
 #include <asm/arch-tegra/board.h>
 #include <asm/arch-tegra/clk_rst.h>
 #include <asm/arch-tegra/pmc.h>
@@ -180,6 +181,14 @@ int board_late_init(void)
 	/* Make sure we finish initing the LCD */
 	tegra_lcd_check_next_stage(gd->fdt_blob, 1);
 #endif
+#if defined(CONFIG_TEGRA_SUPPORT_NON_SECURE)
+	if (tegra_cpu_is_non_secure()) {
+		printf("CPU is in NS mode\n");
+		setenv("cpu_ns_mode", "1");
+	} else {
+		setenv("cpu_ns_mode", "");
+	}
+#endif
 	return 0;
 }