ARC: Process-creation/scheduling/idle-loop

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 91 insertions, 0 deletions

diff --git a/arch/arc/kernel/ctx_sw.c b/arch/arc/kernel/ctx_sw.c
new file mode 100644
index 000000000000..647e37a5165e
--- /dev/null
+++ b/arch/arc/kernel/ctx_sw.c
@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Vineetg: Aug 2009
+ *  -"C" version of lowest level context switch asm macro called by schedular
+ *   gcc doesn't generate the dward CFI info for hand written asm, hence can't
+ *   backtrace out of it (e.g. tasks sleeping in kernel).
+ *   So we cheat a bit by writing almost similar code in inline-asm.
+ *  -This is a hacky way of doing things, but there is no other simple way.
+ *   I don't want/intend to extend unwinding code to understand raw asm
+ */
+
+#include <asm/asm-offsets.h>
+#include <linux/sched.h>
+
+struct task_struct *__sched
+__switch_to(struct task_struct *prev_task, struct task_struct *next_task)
+{
+        unsigned int tmp;
+        unsigned int prev = (unsigned int)prev_task;
+        unsigned int next = (unsigned int)next_task;
+        int num_words_to_skip = 1;
+
+        __asm__ __volatile__(
+                /* FP/BLINK save generated by gcc (standard function prologue */
+                "st.a    r13, [sp, -4]   \n\t"
+                "st.a    r14, [sp, -4]   \n\t"
+                "st.a    r15, [sp, -4]   \n\t"
+                "st.a    r16, [sp, -4]   \n\t"
+                "st.a    r17, [sp, -4]   \n\t"
+                "st.a    r18, [sp, -4]   \n\t"
+                "st.a    r19, [sp, -4]   \n\t"
+                "st.a    r20, [sp, -4]   \n\t"
+                "st.a    r21, [sp, -4]   \n\t"
+                "st.a    r22, [sp, -4]   \n\t"
+                "st.a    r23, [sp, -4]   \n\t"
+                "st.a    r24, [sp, -4]   \n\t"
+                "st.a    r25, [sp, -4]   \n\t"
+                "sub     sp, sp, %4      \n\t"  /* create gutter at top */
+
+                /* set ksp of outgoing task in tsk->thread.ksp */
+                "st.as   sp, [%3, %1]    \n\t"
+
+                "sync   \n\t"
+
+                /*
+                 * setup _current_task with incoming tsk.
+                 * optionally, set r25 to that as well
+                 * For SMP extra work to get to &_current_task[cpu]
+                 * (open coded SET_CURR_TASK_ON_CPU)
+                 */
+                "st  %2, [@_current_task]       \n\t"
+
+                /* get ksp of incoming task from tsk->thread.ksp */
+                "ld.as  sp, [%2, %1]   \n\t"
+
+                /* start loading it's CALLEE reg file */
+
+                "add    sp, sp, %4     \n\t"    /* skip gutter at top */
+
+                "ld.ab   r25, [sp, 4]   \n\t"
+                "ld.ab   r24, [sp, 4]   \n\t"
+                "ld.ab   r23, [sp, 4]   \n\t"
+                "ld.ab   r22, [sp, 4]   \n\t"
+                "ld.ab   r21, [sp, 4]   \n\t"
+                "ld.ab   r20, [sp, 4]   \n\t"
+                "ld.ab   r19, [sp, 4]   \n\t"
+                "ld.ab   r18, [sp, 4]   \n\t"
+                "ld.ab   r17, [sp, 4]   \n\t"
+                "ld.ab   r16, [sp, 4]   \n\t"
+                "ld.ab   r15, [sp, 4]   \n\t"
+                "ld.ab   r14, [sp, 4]   \n\t"
+                "ld.ab   r13, [sp, 4]   \n\t"
+
+                /* last (ret value) = prev : although for ARC it mov r0, r0 */
+                "mov     %0, %3        \n\t"
+
+                /* FP/BLINK restore generated by gcc (standard func epilogue */
+
+                : "=r"(tmp)
+                : "n"((TASK_THREAD + THREAD_KSP) / 4), "r"(next), "r"(prev),
+                  "n"(num_words_to_skip * 4)
+                : "blink"
+        );
+
+        return (struct task_struct *)tmp;
+}