[boot-wrapper] [PATCH] aarch64: Enable TRBE for the non-secure world

[Anshuman Khandual]

MDCR_EL3.NSTB resets to an UNKNOWN value. Configure it to allow the trace
buffer to use non-secure memory and to permit direct register accesses from
the non-secure world. Before that, just check AA64DFR0_EL1.TraceBuffer and
make sure TRBE is implemented. We still continue to reset MDCR_EL3 register
to zero with the exception of MDCR_EL3.NSPB and MDCR_EL3.NSTB.

Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
---
 arch/aarch64/boot.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/aarch64/boot.S b/arch/aarch64/boot.S
index 37f4b98..e47cf59 100644
--- a/arch/aarch64/boot.S
+++ b/arch/aarch64/boot.S
@@ -71,6 +71,14 @@ _start:
 	ldr	x1, =(0x3 << 12)
 	orr	x0, x0, x1
 
+1:	mrs	x1, id_aa64dfr0_el1
+	ubfx	x1, x1, #44, #4
+	cbz	x1, 1f
+
+	// Enable TRBE for the non-secure world.
+	ldr	x1, =(0x3 << 24)
+	orr	x0, x0, x1
+
 1:	msr	mdcr_el3, x0			// Disable traps to EL3
 
 	mrs	x0, id_aa64pfr0_el1
-- 
2.7.4