1/*
  2 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
  3 *
  4 * This program is free software; you can redistribute it and/or modify
  5 * it under the terms of the GNU General Public License version 2 as
  6 * published by the Free Software Foundation.
  7 *
  8 * Vineetg: Aug 2009
  9 *  -"C" version of lowest level context switch asm macro called by schedular
 10 *   gcc doesn't generate the dward CFI info for hand written asm, hence can't
 11 *   backtrace out of it (e.g. tasks sleeping in kernel).
 12 *   So we cheat a bit by writing almost similar code in inline-asm.
 13 *  -This is a hacky way of doing things, but there is no other simple way.
 14 *   I don't want/intend to extend unwinding code to understand raw asm
 15 */
 16
 17#include <asm/asm-offsets.h>
 18#include <linux/sched.h>
 19
 20#define KSP_WORD_OFF 	((TASK_THREAD + THREAD_KSP) / 4)
 21
 22struct task_struct *__sched
 23__switch_to(struct task_struct *prev_task, struct task_struct *next_task)
 24{
 25	unsigned int tmp;
 26	unsigned int prev = (unsigned int)prev_task;
 27	unsigned int next = (unsigned int)next_task;
 28
 29	__asm__ __volatile__(
 30		/* FP/BLINK save generated by gcc (standard function prologue */
 31		"st.a    r13, [sp, -4]   \n\t"
 32		"st.a    r14, [sp, -4]   \n\t"
 33		"st.a    r15, [sp, -4]   \n\t"
 34		"st.a    r16, [sp, -4]   \n\t"
 35		"st.a    r17, [sp, -4]   \n\t"
 36		"st.a    r18, [sp, -4]   \n\t"
 37		"st.a    r19, [sp, -4]   \n\t"
 38		"st.a    r20, [sp, -4]   \n\t"
 39		"st.a    r21, [sp, -4]   \n\t"
 40		"st.a    r22, [sp, -4]   \n\t"
 41		"st.a    r23, [sp, -4]   \n\t"
 42		"st.a    r24, [sp, -4]   \n\t"
 43#ifndef CONFIG_ARC_CURR_IN_REG
 44		"st.a    r25, [sp, -4]   \n\t"
 45#else
 46		"sub     sp, sp, 4      \n\t"	/* usual r25 placeholder */
 47#endif
 48
 49		/* set ksp of outgoing task in tsk->thread.ksp */
 50#if KSP_WORD_OFF <= 255
 51		"st.as   sp, [%3, %1]    \n\t"
 52#else
 53		/*
 54		 * Workaround for NR_CPUS=4k
 55		 * %1 is bigger than 255 (S9 offset for st.as)
 56		 */
 57		"add2    r24, %3, %1     \n\t"
 58		"st      sp, [r24]       \n\t"
 59#endif
 60
 61		/*
 62		 * setup _current_task with incoming tsk.
 63		 * optionally, set r25 to that as well
 64		 * For SMP extra work to get to &_current_task[cpu]
 65		 * (open coded SET_CURR_TASK_ON_CPU)
 66		 */
 67#ifndef CONFIG_SMP
 68		"st  %2, [@_current_task]	\n\t"
 69#else
 70		"lr   r24, [identity]		\n\t"
 71		"lsr  r24, r24, 8		\n\t"
 72		"bmsk r24, r24, 7		\n\t"
 73		"add2 r24, @_current_task, r24	\n\t"
 74		"st   %2,  [r24]		\n\t"
 75#endif
 76#ifdef CONFIG_ARC_CURR_IN_REG
 77		"mov r25, %2   \n\t"
 78#endif
 79
 80		/* get ksp of incoming task from tsk->thread.ksp */
 81		"ld.as  sp, [%2, %1]   \n\t"
 82
 83		/* start loading it's CALLEE reg file */
 84
 85#ifndef CONFIG_ARC_CURR_IN_REG
 86		"ld.ab   r25, [sp, 4]   \n\t"
 87#else
 88		"add    sp, sp, 4       \n\t"
 89#endif
 90		"ld.ab   r24, [sp, 4]   \n\t"
 91		"ld.ab   r23, [sp, 4]   \n\t"
 92		"ld.ab   r22, [sp, 4]   \n\t"
 93		"ld.ab   r21, [sp, 4]   \n\t"
 94		"ld.ab   r20, [sp, 4]   \n\t"
 95		"ld.ab   r19, [sp, 4]   \n\t"
 96		"ld.ab   r18, [sp, 4]   \n\t"
 97		"ld.ab   r17, [sp, 4]   \n\t"
 98		"ld.ab   r16, [sp, 4]   \n\t"
 99		"ld.ab   r15, [sp, 4]   \n\t"
100		"ld.ab   r14, [sp, 4]   \n\t"
101		"ld.ab   r13, [sp, 4]   \n\t"
102
103		/* last (ret value) = prev : although for ARC it mov r0, r0 */
104		"mov     %0, %3        \n\t"
105
106		/* FP/BLINK restore generated by gcc (standard func epilogue */
107
108		: "=r"(tmp)
109		: "n"(KSP_WORD_OFF), "r"(next), "r"(prev)
110		: "blink"
111	);
112
113	return (struct task_struct *)tmp;
114}