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>

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;
+}