ARM: add secure monitor handler to switch to non-secure state

A prerequisite for using virtualization is to be in HYP mode, which
requires the CPU to be in non-secure state first.
Add a new file in arch/arm/cpu/armv7 to hold a monitor handler routine
which switches the CPU to non-secure state by setting the NS and
associated bits.
According to the ARM architecture reference manual this should not be
done in SVC mode, so we have to setup a SMC handler for this.
We create a new vector table to avoid interference with other boards.
The MVBAR register will be programmed later just before the smc call.

Signed-off-by: Andre Przywara <andre.przywara@linaro.org>

arch/arm/cpu/armv7/Makefile

@@ -20,6 +20,10 @@ ifneq ($(CONFIG_AM43XX)$(CONFIG_AM33XX)$(CONFIG_OMAP44XX)$(CONFIG_OMAP54XX)$(CON
 SOBJS	+= lowlevel_init.o
 endif
 
+ifneq ($(CONFIG_ARMV7_NONSEC),)
+SOBJS	+= nonsec_virt.o
+endif
+
 SRCS	:= $(START:.o=.S) $(COBJS:.o=.c)
 OBJS	:= $(addprefix $(obj),$(COBJS) $(SOBJS))
 START	:= $(addprefix $(obj),$(START))

arch/arm/cpu/armv7/nonsec_virt.S

@@ -0,0 +1,53 @@
+/*
+ * code for switching cores into non-secure state
+ *
+ * Copyright (c) 2013	Andre Przywara <andre.przywara@linaro.org>
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+#include <config.h>
+
+/* the vector table for secure state */
+_monitor_vectors:
+	.word 0	/* reset */
+	.word 0 /* undef */
+	adr pc, _secure_monitor
+	.word 0
+	.word 0
+	.word 0
+	.word 0
+	.word 0
+
+/*
+ * secure monitor handler
+ * U-boot calls this "software interrupt" in start.S
+ * This is executed on a "smc" instruction, we use a "smc #0" to switch
+ * to non-secure state.
+ * We use only r0 and r1 here, due to constraints in the caller.
+ */
+	.align	5
+_secure_monitor:
+	mrc	p15, 0, r1, c1, c1, 0		@ read SCR
+	bic	r1, r1, #0x4e			@ clear IRQ, FIQ, EA, nET bits
+	orr	r1, r1, #0x31			@ enable NS, AW, FW bits
+
+	mcr	p15, 0, r1, c1, c1, 0		@ write SCR (with NS bit set)
+
+	movs	pc, lr				@ return to non-secure SVC