ARM: add assembly routine to switch to non-secure state

While actually switching to non-secure state is one thing, another
part of this process is to make sure that we still have full access
to the interrupt controller (GIC).
The GIC is fully aware of secure vs. non-secure state, some
registers are banked, others may be configured to be accessible from
secure state only.
To be as generic as possible, we get the GIC memory mapped address
based on the PERIPHBASE value in the CBAR register. Since this
register is not architecturally defined, we check the MIDR before to
be from an A15 or A7.
For CPUs not having the CBAR or boards with wrong information herein
we allow providing the base address as a configuration variable.

Now that we know the GIC address, we:
a) allow private interrupts to be delivered to the core
   (GICD_IGROUPR0 = 0xFFFFFFFF)
b) enable the CPU interface (GICC_CTLR[0] = 1)
c) set the priority filter to allow non-secure interrupts
   (GICC_PMR = 0xFF)

Also we allow access to all coprocessor interfaces from non-secure
state by writing the appropriate bits in the NSACR register.

The generic timer base frequency register is only accessible from
secure state, so we have to program it now. Actually this should be
done from primary firmware before, but some boards seems to omit
this, so if needed we do this here with a board specific value.
The Versatile Express board does not need this, so we remove the
frequency from the configuration file here.

After having switched to non-secure state, we also enable the
non-secure GIC CPU interface, since this register is banked.

Since we need to call this routine also directly from the smp_pen
later (where we don't have any stack), we can only use caller saved
registers r0-r3 and r12 to not mess with the compiler.

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

1 files changed, 87 insertions, 0 deletions

diff --git a/arch/arm/cpu/armv7/nonsec_virt.S b/arch/arm/cpu/armv7/nonsec_virt.S
index d11eb2dc63..3dd60b7137 100644
--- a/arch/arm/cpu/armv7/nonsec_virt.S
+++ b/arch/arm/cpu/armv7/nonsec_virt.S
@@ -23,6 +23,11 @@
  */
 
 #include <config.h>
+#include <linux/linkage.h>
+#include <asm/gic.h>
+#include <asm/armv7.h>
+
+.arch_extension sec
 
 /* the vector table for secure state */
 _monitor_vectors:
@@ -51,3 +56,85 @@ _secure_monitor:
 	mcr	p15, 0, r1, c1, c1, 0		@ write SCR (with NS bit set)
 
 	movs	pc, lr				@ return to non-secure SVC
+
+/*
+ * Switch a core to non-secure state.
+ *
+ *  1. initialize the GIC per-core interface
+ *  2. allow coprocessor access in non-secure modes
+ *  3. switch the cpu mode (by calling "smc #0")
+ *
+ * Called from smp_pen by secondary cores and directly by the BSP.
+ * Do not assume that the stack is available and only use registers
+ * r0-r3 and r12.
+ *
+ * PERIPHBASE is used to get the GIC address. This could be 40 bits long,
+ * though, but we check this in C before calling this function.
+ */
+ENTRY(_nonsec_init)
+#ifdef CONFIG_ARM_GIC_BASE_ADDRESS
+	ldr	r2, =CONFIG_ARM_GIC_BASE_ADDRESS
+#else
+	mrc	p15, 4, r2, c15, c0, 0		@ read CBAR
+	bfc	r2, #0, #15			@ clear reserved bits
+#endif
+	add	r3, r2, #GIC_DIST_OFFSET	@ GIC dist i/f offset
+	mvn	r1, #0				@ all bits to 1
+	str	r1, [r3, #GICD_IGROUPRn]	@ allow private interrupts
+
+	mrc	p15, 0, r0, c0, c0, 0		@ read MIDR
+	ldr	r1, =MIDR_PRIMARY_PART_MASK
+	and	r0, r0, r1			@ mask out variant and revision
+
+	ldr	r1, =MIDR_CORTEX_A7_R0P0 & MIDR_PRIMARY_PART_MASK
+	cmp	r0, r1				@ check for Cortex-A7
+
+	ldr	r1, =MIDR_CORTEX_A15_R0P0 & MIDR_PRIMARY_PART_MASK
+	cmpne	r0, r1				@ check for Cortex-A15
+
+	movne	r1, #GIC_CPU_OFFSET_A9		@ GIC CPU offset for A9
+	moveq	r1, #GIC_CPU_OFFSET_A15		@ GIC CPU offset for A15/A7
+	add	r3, r2, r1			@ r3 = GIC CPU i/f addr
+
+	mov	r1, #1				@ set GICC_CTLR[enable]
+	str	r1, [r3, #GICC_CTLR]		@ and clear all other bits
+	mov	r1, #0xff
+	str	r1, [r3, #GICC_PMR]		@ set priority mask register
+
+	movw	r1, #0x3fff
+	movt	r1, #0x0006
+	mcr	p15, 0, r1, c1, c1, 2		@ NSACR = all copros to non-sec
+
+/* The CNTFRQ register of the generic timer needs to be
+ * programmed in secure state. Some primary bootloaders / firmware
+ * omit this, so if the frequency is provided in the configuration,
+ * we do this here instead.
+ * But first check if we have the generic timer.
+ */
+#ifdef CONFIG_SYS_CLK_FREQ
+	mrc	p15, 0, r0, c0, c1, 1		@ read ID_PFR1
+	and	r0, r0, #CPUID_ARM_GENTIMER_MASK	@ mask arch timer bits
+	cmp	r0, #(1 << CPUID_ARM_GENTIMER_SHIFT)
+	ldreq	r1, =CONFIG_SYS_CLK_FREQ
+	mcreq	p15, 0, r1, c14, c0, 0		@ write CNTFRQ
+#endif
+
+	adr	r1, _monitor_vectors
+	mcr	p15, 0, r1, c12, c0, 1		@ set MVBAR to secure vectors
+
+	mrc	p15, 0, ip, c12, c0, 0		@ save secure copy of VBAR
+
+	isb
+	smc	#0				@ call into MONITOR mode
+
+	mcr	p15, 0, ip, c12, c0, 0		@ write non-secure copy of VBAR
+
+	mov	r1, #1
+	str	r1, [r3, #GICC_CTLR]		@ enable non-secure CPU i/f
+	add	r2, r2, #GIC_DIST_OFFSET
+	str	r1, [r2, #GICD_CTLR]		@ allow private interrupts
+
+	mov	r0, r3				@ return GICC address
+
+	bx	lr
+ENDPROC(_nonsec_init)