ARM: add C function to switch to non-secure state

The core specific part of the work is done in the assembly routine
in nonsec_virt.S, introduced with the previous patch, but for the full
glory we need to setup the GIC distributor interface once for the
whole system, which is done in C here.
The routine is placed in arch/arm/cpu/armv7 to allow easy access from
other ARMv7 boards.

We check the availability of the security extensions first.

Since we need a safe way to access the GIC, we use the PERIPHBASE
registers on Cortex-A15 and A7 CPUs and do some sanity checks.
Boards not implementing the CBAR can override this value via a
configuration file variable.

Then we actually do the GIC enablement:
a) enable the GIC distributor, both for non-secure and secure state
   (GICD_CTLR[1:0] = 11b)
b) allow all interrupts to be handled from non-secure state
   (GICD_IGROUPRn = 0xFFFFFFFF)

The core specific GIC setup is then done in the assembly routine.
Signed-off-by: NAndre Przywara <andre.przywara@linaro.org>

arch/arm/cpu/armv7/Makefile

@@ -22,6 +22,7 @@ endif
 
 ifneq ($(CONFIG_ARMV7_NONSEC),)
 SOBJS	+= nonsec_virt.o
+COBJS	+= virt-v7.o
 endif
 
 SRCS	:= $(START:.o=.S) $(COBJS:.o=.c)

arch/arm/cpu/armv7/virt-v7.c

+/*
+ * (C) Copyright 2013
+ * Andre Przywara, Linaro
+ *
+ * Routines to transition ARMv7 processors from secure into non-secure state
+ * needed to enable ARMv7 virtualization for current hypervisors
+ *
+ * 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 <common.h>
+#include <asm/armv7.h>
+#include <asm/gic.h>
+#include <asm/io.h>
+
+unsigned long gic_dist_addr;
+
+static unsigned int read_id_pfr1(void)
+{
+	unsigned int reg;
+
+	asm("mrc p15, 0, %0, c0, c1, 1\n" : "=r"(reg));
+	return reg;
+}
+
+static unsigned long get_gicd_base_address(void)
+{
+#ifdef CONFIG_ARM_GIC_BASE_ADDRESS
+	return CONFIG_ARM_GIC_BASE_ADDRESS + GIC_DIST_OFFSET;
+#else
+	unsigned midr;
+	unsigned periphbase;
+
+	/* check whether we are an Cortex-A15 or A7.
+	 * The actual HYP switch should work with all CPUs supporting
+	 * the virtualization extension, but we need the GIC address,
+	 * which we know only for sure for those two CPUs.
+	 */
+	asm("mrc p15, 0, %0, c0, c0, 0\n" : "=r"(midr));
+	switch (midr & MIDR_PRIMARY_PART_MASK) {
+	case MIDR_CORTEX_A9_R0P1:
+	case MIDR_CORTEX_A15_R0P0:
+	case MIDR_CORTEX_A7_R0P0:
+		break;
+	default:
+		printf("nonsec: could not determine GIC address.\n");
+		return -1;
+	}
+
+	/* get the GIC base address from the CBAR register */
+	asm("mrc p15, 4, %0, c15, c0, 0\n" : "=r" (periphbase));
+
+	/* the PERIPHBASE can be mapped above 4 GB (lower 8 bits used to
+	 * encode this). Bail out here since we cannot access this without
+	 * enabling paging.
+	 */
+	if ((periphbase & 0xff) != 0) {
+		printf("nonsec: PERIPHBASE is above 4 GB, no access.\n");
+		return -1;
+	}
+
+	return (periphbase & CBAR_MASK) + GIC_DIST_OFFSET;
+#endif
+}
+
+int armv7_switch_nonsec(void)
+{
+	unsigned int reg;
+	unsigned itlinesnr, i;
+
+	/* check whether the CPU supports the security extensions */
+	reg = read_id_pfr1();
+	if ((reg & 0xF0) == 0) {
+		printf("nonsec: Security extensions not implemented.\n");
+		return -1;
+	}
+
+	/* the SCR register will be set directly in the monitor mode handler,
+	 * according to the spec one should not tinker with it in secure state
+	 * in SVC mode. Do not try to read it once in non-secure state,
+	 * any access to it will trap.
+	 */
+
+	gic_dist_addr = get_gicd_base_address();
+	if (gic_dist_addr == -1)
+		return -1;
+
+	/* enable the GIC distributor */
+	writel(readl(gic_dist_addr + GICD_CTLR) | 0x03,
+	       gic_dist_addr + GICD_CTLR);
+
+	/* TYPER[4:0] contains an encoded number of available interrupts */
+	itlinesnr = readl(gic_dist_addr + GICD_TYPER) & 0x1f;
+
+	/* set all bits in the GIC group registers to one to allow access
+	 * from non-secure state. The first 32 interrupts are private per
+	 * CPU and will be set later when enabling the GIC for each core
+	 */
+	for (i = 1; i <= itlinesnr; i++)
+		writel((unsigned)-1, gic_dist_addr + GICD_IGROUPRn + 4 * i);
+
+	/* call the non-sec switching code on this CPU */
+	_nonsec_init();
+
+	return 0;
+}

arch/arm/include/asm/armv7.h

@@ -77,6 +77,9 @@ void v7_outer_cache_flush_range(u32 start, u32 end);
 void v7_outer_cache_inval_range(u32 start, u32 end);
 
 #ifdef CONFIG_ARMV7_NONSEC
+
+int armv7_switch_nonsec(void);
+
 /* defined in assembly file */
 unsigned int _nonsec_init(void);
 #endif /* CONFIG_ARMV7_NONSEC */