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, 5 insertions, 1 deletions

diff --git a/arch/arm/mach-tegra/clock.c b/arch/arm/mach-tegra/clock.c
index 11c7435..7c274b5 100644
--- a/arch/arm/mach-tegra/clock.c
+++ b/arch/arm/mach-tegra/clock.c
@@ -20,6 +20,7 @@
 #include <asm/io.h>
 #include <asm/arch/clock.h>
 #include <asm/arch/tegra.h>
+#include <asm/arch-tegra/ap.h>
 #include <asm/arch-tegra/clk_rst.h>
 #include <asm/arch-tegra/timer.h>
 #include <div64.h>
@@ -573,7 +574,10 @@ void clock_init(void)
 	debug("PLLX = %d\n", pll_rate[CLOCK_ID_XCPU]);
 
 	/* Do any special system timer/TSC setup */
-	arch_timer_init();
+#if defined(CONFIG_TEGRA_SUPPORT_NON_SECURE)
+	if (!tegra_cpu_is_non_secure())
+#endif
+		arch_timer_init();
 }
 
 static void set_avp_clock_source(u32 src)