1 files changed, 106 insertions, 0 deletions
diff --git a/src/soc/qualcomm/ipq806x/tz_wrapper.S b/src/soc/qualcomm/ipq806x/tz_wrapper.S
new file mode 100644
index 0000000000..70cc170f64
--- /dev/null
+++ b/src/soc/qualcomm/ipq806x/tz_wrapper.S
@@ -0,0 +1,106 @@
+/*
+ * Copyright (c) 2014, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * 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.
+ */
+
+/*
+ * TZ expects the ARM core to be in 'ARM' mode. However, coreboot seems
+ * to be compiled in mixed thumb/arm mode. Hence create a glue function
+ * to invoke TZ.
+ */
+
+#include <arch/asm.h>
+
+/*
+ * Force ARM mode. Else this gets assembled with mixed ARM and
+ * Thumb instructions. We set up everything and jump to TZBSP
+ * using the 'blx' instruction. For 'blx' if the last bit of the
+ * destination address is zero, it switches to ARM mode. Since,
+ * we are already in ARM mode, nothing to switch as such.
+ *
+ * However, when TZBSP returns, the CPU is still in ARM mode.
+ * If the assembler inserts Thumb instructions between the point
+ * of return from TZBSP to the 'bx' instruction we are hosed.
+ * Hence forcing ARM mode.
+ *
+ * Rest of the code can be compiled in mixed ARM/Thumb mode.
+ * Since tz_init_wrapper is being forced as an ARM symbol,
+ * callers will use 'blx' to come here forcing a switch to
+ * ARM mode. The wrapper does its job and returns back to the
+ * Thumb caller.
+ */
+.arm
+/*
+ * int tz_init_wrapper(int, int, void *);
+ */
+ENTRY(tz_init_wrapper)
+	.global tz_init_wrapper
+
+	/*
+	 *      r0 = tz_arg1
+	 *      r1 = tz_arg2
+	 *      r2 = tz_load_addr
+	 */
+
+	/*
+	 * Per the AAPCS
+	 *	r0, r1, r2, r3, r12 can be clobbered
+	 *	r4, r5, r6, r7, r8, r9, r10, r11 have to be preserved
+	 *
+	 * Following code clobbers
+	 *	r0 - Setting return value to zero
+	 *	r1 - For doing a thumb return
+	 *	r3 - Passing 'SP' from current mode to 'svc' mode
+	 *	r4 - To save & restore CPSR
+	 *
+	 * Per AAPCS, save and restore r4, rest are 'clobberable' :)
+	 * The invoked code takes care of saving and restoring the other
+	 * preserved registers (i.e. r5 - r11)
+	 *
+	 * Stack Usage:
+	 *	SP ->	| LR	|	(Lower address)
+	 *		| r4	|
+	 *		| CPSR	|
+	 *		|-------|
+	 *		|   .   |
+	 *		|   .   |
+	 *		|   .   |	(Higher address)
+	 */
+
+	sub	sp, sp, #12	/* Allocate stack frame */
+	str	lr, [sp]	/* Save return address */
+	str	r4, [sp, #4]	/* Use r4 to hold the new CPSR value */
+
+	mov	r3, sp		/* Get current stack pointer */
+
+	mrs	r4, CPSR	/* save CPSR */
+	str	r4, [sp, #8]
+
+	bic	r4, r4, 0x1f	/* Clear mode bits */
+	orr	r4, r4, 0x13	/* 'svc' mode */
+	msr	cpsr_cxf, r4	/* Switch to Supervisor mode. */
+	mov	sp, r3		/* Use the same stack as the previous mode */
+
+	blx	r2		/* Jump to TZ in ARM mode */
+
+	nop			/* back from TZ, in ARM mode */
+
+	ldr	r4, [sp, #8]	/* restore CPSR */
+	msr	cpsr_cxf, r4
+
+	ldr	r4, [sp, #4]	/* restore r4 */
+
+	ldr	lr, [sp]	/* saved return address */
+	add	sp, sp, #12	/* free stack frame */
+
+	bx	lr		/* back to thumb caller */
+
+ENDPROC(tz_init_wrapper)