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
22 struct task_struct *__sched
__switch_to(struct task_struct * prev_task,struct task_struct * next_task)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 "sync \n\t"
62
63 /*
64 * setup _current_task with incoming tsk.
65 * optionally, set r25 to that as well
66 * For SMP extra work to get to &_current_task[cpu]
67 * (open coded SET_CURR_TASK_ON_CPU)
68 */
69 #ifndef CONFIG_SMP
70 "st %2, [@_current_task] \n\t"
71 #else
72 "lr r24, [identity] \n\t"
73 "lsr r24, r24, 8 \n\t"
74 "bmsk r24, r24, 7 \n\t"
75 "add2 r24, @_current_task, r24 \n\t"
76 "st %2, [r24] \n\t"
77 #endif
78 #ifdef CONFIG_ARC_CURR_IN_REG
79 "mov r25, %2 \n\t"
80 #endif
81
82 /* get ksp of incoming task from tsk->thread.ksp */
83 "ld.as sp, [%2, %1] \n\t"
84
85 /* start loading it's CALLEE reg file */
86
87 #ifndef CONFIG_ARC_CURR_IN_REG
88 "ld.ab r25, [sp, 4] \n\t"
89 #else
90 "add sp, sp, 4 \n\t"
91 #endif
92 "ld.ab r24, [sp, 4] \n\t"
93 "ld.ab r23, [sp, 4] \n\t"
94 "ld.ab r22, [sp, 4] \n\t"
95 "ld.ab r21, [sp, 4] \n\t"
96 "ld.ab r20, [sp, 4] \n\t"
97 "ld.ab r19, [sp, 4] \n\t"
98 "ld.ab r18, [sp, 4] \n\t"
99 "ld.ab r17, [sp, 4] \n\t"
100 "ld.ab r16, [sp, 4] \n\t"
101 "ld.ab r15, [sp, 4] \n\t"
102 "ld.ab r14, [sp, 4] \n\t"
103 "ld.ab r13, [sp, 4] \n\t"
104
105 /* last (ret value) = prev : although for ARC it mov r0, r0 */
106 "mov %0, %3 \n\t"
107
108 /* FP/BLINK restore generated by gcc (standard func epilogue */
109
110 : "=r"(tmp)
111 : "n"(KSP_WORD_OFF), "r"(next), "r"(prev)
112 : "blink"
113 );
114
115 return (struct task_struct *)tmp;
116 }
117