1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
  4 *
  5 * Vineetg: Aug 2009
  6 *  -"C" version of lowest level context switch asm macro called by schedular
  7 *   gcc doesn't generate the dward CFI info for hand written asm, hence can't
  8 *   backtrace out of it (e.g. tasks sleeping in kernel).
  9 *   So we cheat a bit by writing almost similar code in inline-asm.
 10 *  -This is a hacky way of doing things, but there is no other simple way.
 11 *   I don't want/intend to extend unwinding code to understand raw asm
 12 */
 13
 14#include <asm/asm-offsets.h>
 15#include <linux/sched.h>
 16#include <linux/sched/debug.h>
 17
 18#define KSP_WORD_OFF 	((TASK_THREAD + THREAD_KSP) / 4)
 19
 20struct task_struct *__sched
 21__switch_to(struct task_struct *prev_task, struct task_struct *next_task)
 22{
 23	unsigned int tmp;
 24	unsigned int prev = (unsigned int)prev_task;
 25	unsigned int next = (unsigned int)next_task;
 26
 27	__asm__ __volatile__(
 28		/* FP/BLINK save generated by gcc (standard function prologue */
 29		"st.a    r13, [sp, -4]   \n\t"
 30		"st.a    r14, [sp, -4]   \n\t"
 31		"st.a    r15, [sp, -4]   \n\t"
 32		"st.a    r16, [sp, -4]   \n\t"
 33		"st.a    r17, [sp, -4]   \n\t"
 34		"st.a    r18, [sp, -4]   \n\t"
 35		"st.a    r19, [sp, -4]   \n\t"
 36		"st.a    r20, [sp, -4]   \n\t"
 37		"st.a    r21, [sp, -4]   \n\t"
 38		"st.a    r22, [sp, -4]   \n\t"
 39		"st.a    r23, [sp, -4]   \n\t"
 40		"st.a    r24, [sp, -4]   \n\t"
 41#ifndef CONFIG_ARC_CURR_IN_REG
 42		"st.a    r25, [sp, -4]   \n\t"
 43#else
 44		"sub     sp, sp, 4      \n\t"	/* usual r25 placeholder */
 45#endif
 46
 47		/* set ksp of outgoing task in tsk->thread.ksp */
 48#if KSP_WORD_OFF <= 255
 49		"st.as   sp, [%3, %1]    \n\t"
 50#else
 51		/*
 52		 * Workaround for NR_CPUS=4k
 53		 * %1 is bigger than 255 (S9 offset for st.as)
 54		 */
 55		"add2    r24, %3, %1     \n\t"
 56		"st      sp, [r24]       \n\t"
 57#endif
 58
 59		/*
 60		 * setup _current_task with incoming tsk.
 61		 * optionally, set r25 to that as well
 62		 * For SMP extra work to get to &_current_task[cpu]
 63		 * (open coded SET_CURR_TASK_ON_CPU)
 64		 */
 65#ifndef CONFIG_SMP
 66		"st  %2, [@_current_task]	\n\t"
 67#else
 68		"lr   r24, [identity]		\n\t"
 69		"lsr  r24, r24, 8		\n\t"
 70		"bmsk r24, r24, 7		\n\t"
 71		"add2 r24, @_current_task, r24	\n\t"
 72		"st   %2,  [r24]		\n\t"
 73#endif
 74#ifdef CONFIG_ARC_CURR_IN_REG
 75		"mov r25, %2   \n\t"
 76#endif
 77
 78		/* get ksp of incoming task from tsk->thread.ksp */
 79		"ld.as  sp, [%2, %1]   \n\t"
 80
 81		/* start loading it's CALLEE reg file */
 82
 83#ifndef CONFIG_ARC_CURR_IN_REG
 84		"ld.ab   r25, [sp, 4]   \n\t"
 85#else
 86		"add    sp, sp, 4       \n\t"
 87#endif
 88		"ld.ab   r24, [sp, 4]   \n\t"
 89		"ld.ab   r23, [sp, 4]   \n\t"
 90		"ld.ab   r22, [sp, 4]   \n\t"
 91		"ld.ab   r21, [sp, 4]   \n\t"
 92		"ld.ab   r20, [sp, 4]   \n\t"
 93		"ld.ab   r19, [sp, 4]   \n\t"
 94		"ld.ab   r18, [sp, 4]   \n\t"
 95		"ld.ab   r17, [sp, 4]   \n\t"
 96		"ld.ab   r16, [sp, 4]   \n\t"
 97		"ld.ab   r15, [sp, 4]   \n\t"
 98		"ld.ab   r14, [sp, 4]   \n\t"
 99		"ld.ab   r13, [sp, 4]   \n\t"
100
101		/* last (ret value) = prev : although for ARC it mov r0, r0 */
102		"mov     %0, %3        \n\t"
103
104		/* FP/BLINK restore generated by gcc (standard func epilogue */
105
106		: "=r"(tmp)
107		: "n"(KSP_WORD_OFF), "r"(next), "r"(prev)
108		: "blink"
109	);
110
111	return (struct task_struct *)tmp;
112}