arm64: Provide secmon trampoline for restart

If an exception is taken that the secmon won't return
to, there needs to be way to reset that cpu's state
w.r.t. stack usage. Therefore, provide secmon_trampoline
which will reinitialize the exception stack and SP_EL0
and start executing with SP_EL0 like the initial state
of the secmon entry.

BUG=chrome-os-partner:30785
BRANCH=None
TEST=Built and booted to kernel. Also tested when PSCI
     is employed in the kernel.

Change-Id: Ie9f5bbe715dcbcf8b67ea40f9a3a5088ac7aa2ad
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: f1f546ee3e9eca93baaa1ae0437351205bf548a5
Original-Change-Id: Ia3da75e1fa0251c8ea30eb0b0523c8a51c03b917
Original-Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/218922
Original-Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: http://review.coreboot.org/9096
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins)

src/arch/arm64/armv8/secmon/Makefile.inc

@@ -33,6 +33,7 @@ secmon-S-ccopts += -I$(src)/arch/arm64/include/armv8/ -include $(src)/include/kc
 
 secmon-y += secmon_init.c
 secmon-y += smc.c
+secmon-y += trampoline.S
 secmon-y += ../exception.c
 secmon-y += ../../cpu.c
 secmon-y += ../../transition_asm.S ../../transition.c

src/arch/arm64/armv8/secmon/secmon.h

@@ -0,0 +1,34 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2014 Google Inc
+ *
+ * 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; version 2 of
+ * the License.
+ *
+ * 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., 51 Franklin St, Fifth Floor, Boston,
+ * MA 02110-1301 USA
+ */
+
+#ifndef __SECMON_SECMON_H__
+#define __SECMON_SECMON_H__
+
+/*
+ * The secmon_trampoline() switches mode to EL3t, reinitializing both
+ * EL3t and EL3h stacks.
+ */
+void secmon_trampoline(void *entry, void *arg);
+
+/* Wait for action to take place. */
+void secmon_wait_for_action(void);
+
+#endif /* __SECMON_SECMON_H__ */

src/arch/arm64/armv8/secmon/secmon_init.c

@@ -29,6 +29,7 @@
 #include <console/console.h>
 #include <rmodule.h>
 #include <stddef.h>
+#include "secmon.h"
 
 static void cpu_init(int bsp)
 {
@@ -62,7 +63,11 @@ static void secmon_init(struct secmon_params *params, int bsp)
 
 		transition_with_entry(params->entry, params->arg, &exc_state);
 	}
+	secmon_wait_for_action();
+}
 
+void secmon_wait_for_action(void)
+{
 	arch_cpu_wait_for_action();
 }
 

src/arch/arm64/armv8/secmon/trampoline.S

@@ -0,0 +1,51 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2014 Google Inc.
+ *
+ * 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; version 2 of the License.
+ *
+ * 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <arch/asm.h>
+
+/*
+ * Call entry(arg) after reinitializing stack state.
+ * void secmon_trampoline(void *entry, void *arg);
+ */
+ENTRY(secmon_trampoline)
+	mov	x22, x0			/* x22 = function pointer */
+	mov	x23, x1			/* x23 = argument */
+	bl	smp_processor_id	/* x0 = cpu */
+	mov	x24, x0
+
+	/* Set the exception stack for this cpu. */
+	bl	cpu_get_exception_stack
+	msr	SPSel, #1
+	isb
+	mov	sp, x0
+
+	/* Have stack pointer use SP_EL0. */
+	msr	SPSel, #0
+	isb
+
+	/* Set stack for this cpu. */
+	mov	x0, x24		/* x0 = cpu */
+	bl	cpu_get_stack
+	mov	sp, x0
+
+	/* Call the function with specified argument. */
+	mov	x1, x22
+	mov	x0, x23
+	br	x1
+ENDPROC(secmon_trampoline)