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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#ifdef CONFIG_ARC_PLAT_EZNPS
18#include <plat/ctop.h>
19#endif
20
21#define KSP_WORD_OFF ((TASK_THREAD + THREAD_KSP) / 4)
22
23struct task_struct *__sched
24__switch_to(struct task_struct *prev_task, struct task_struct *next_task)
25{
26 unsigned int tmp;
27 unsigned int prev = (unsigned int)prev_task;
28 unsigned int next = (unsigned int)next_task;
29
30 __asm__ __volatile__(
31 /* FP/BLINK save generated by gcc (standard function prologue */
32 "st.a r13, [sp, -4] \n\t"
33 "st.a r14, [sp, -4] \n\t"
34 "st.a r15, [sp, -4] \n\t"
35 "st.a r16, [sp, -4] \n\t"
36 "st.a r17, [sp, -4] \n\t"
37 "st.a r18, [sp, -4] \n\t"
38 "st.a r19, [sp, -4] \n\t"
39 "st.a r20, [sp, -4] \n\t"
40 "st.a r21, [sp, -4] \n\t"
41 "st.a r22, [sp, -4] \n\t"
42 "st.a r23, [sp, -4] \n\t"
43 "st.a r24, [sp, -4] \n\t"
44#ifndef CONFIG_ARC_CURR_IN_REG
45 "st.a r25, [sp, -4] \n\t"
46#else
47 "sub sp, sp, 4 \n\t" /* usual r25 placeholder */
48#endif
49
50 /* set ksp of outgoing task in tsk->thread.ksp */
51#if KSP_WORD_OFF <= 255
52 "st.as sp, [%3, %1] \n\t"
53#else
54 /*
55 * Workaround for NR_CPUS=4k
56 * %1 is bigger than 255 (S9 offset for st.as)
57 */
58 "add2 r24, %3, %1 \n\t"
59 "st sp, [r24] \n\t"
60#endif
61
62 /*
63 * setup _current_task with incoming tsk.
64 * optionally, set r25 to that as well
65 * For SMP extra work to get to &_current_task[cpu]
66 * (open coded SET_CURR_TASK_ON_CPU)
67 */
68#ifndef CONFIG_SMP
69 "st %2, [@_current_task] \n\t"
70#else
71#ifdef CONFIG_ARC_PLAT_EZNPS
72 "lr r24, [%4] \n\t"
73#ifndef CONFIG_EZNPS_MTM_EXT
74 "lsr r24, r24, 4 \n\t"
75#endif
76#else
77 "lr r24, [identity] \n\t"
78 "lsr r24, r24, 8 \n\t"
79 "bmsk r24, r24, 7 \n\t"
80#endif
81 "add2 r24, @_current_task, r24 \n\t"
82 "st %2, [r24] \n\t"
83#endif
84#ifdef CONFIG_ARC_CURR_IN_REG
85 "mov r25, %2 \n\t"
86#endif
87
88 /* get ksp of incoming task from tsk->thread.ksp */
89 "ld.as sp, [%2, %1] \n\t"
90
91 /* start loading it's CALLEE reg file */
92
93#ifndef CONFIG_ARC_CURR_IN_REG
94 "ld.ab r25, [sp, 4] \n\t"
95#else
96 "add sp, sp, 4 \n\t"
97#endif
98 "ld.ab r24, [sp, 4] \n\t"
99 "ld.ab r23, [sp, 4] \n\t"
100 "ld.ab r22, [sp, 4] \n\t"
101 "ld.ab r21, [sp, 4] \n\t"
102 "ld.ab r20, [sp, 4] \n\t"
103 "ld.ab r19, [sp, 4] \n\t"
104 "ld.ab r18, [sp, 4] \n\t"
105 "ld.ab r17, [sp, 4] \n\t"
106 "ld.ab r16, [sp, 4] \n\t"
107 "ld.ab r15, [sp, 4] \n\t"
108 "ld.ab r14, [sp, 4] \n\t"
109 "ld.ab r13, [sp, 4] \n\t"
110
111 /* last (ret value) = prev : although for ARC it mov r0, r0 */
112 "mov %0, %3 \n\t"
113
114 /* FP/BLINK restore generated by gcc (standard func epilogue */
115
116 : "=r"(tmp)
117 : "n"(KSP_WORD_OFF), "r"(next), "r"(prev)
118#ifdef CONFIG_ARC_PLAT_EZNPS
119 , "i"(CTOP_AUX_LOGIC_GLOBAL_ID)
120#endif
121 : "blink"
122 );
123
124 return (struct task_struct *)tmp;
125}