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 #ifdef CONFIG_ARC_PLAT_EZNPS
20 #include <plat/ctop.h>
21 #endif
22
23 #define KSP_WORD_OFF ((TASK_THREAD + THREAD_KSP) / 4)
24
25 struct task_struct *__sched
__switch_to(struct task_struct * prev_task,struct task_struct * next_task)26 __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
27 {
28 unsigned int tmp;
29 unsigned int prev = (unsigned int)prev_task;
30 unsigned int next = (unsigned int)next_task;
31
32 __asm__ __volatile__(
33 /* FP/BLINK save generated by gcc (standard function prologue */
34 "st.a r13, [sp, -4] \n\t"
35 "st.a r14, [sp, -4] \n\t"
36 "st.a r15, [sp, -4] \n\t"
37 "st.a r16, [sp, -4] \n\t"
38 "st.a r17, [sp, -4] \n\t"
39 "st.a r18, [sp, -4] \n\t"
40 "st.a r19, [sp, -4] \n\t"
41 "st.a r20, [sp, -4] \n\t"
42 "st.a r21, [sp, -4] \n\t"
43 "st.a r22, [sp, -4] \n\t"
44 "st.a r23, [sp, -4] \n\t"
45 "st.a r24, [sp, -4] \n\t"
46 #ifndef CONFIG_ARC_CURR_IN_REG
47 "st.a r25, [sp, -4] \n\t"
48 #else
49 "sub sp, sp, 4 \n\t" /* usual r25 placeholder */
50 #endif
51
52 /* set ksp of outgoing task in tsk->thread.ksp */
53 #if KSP_WORD_OFF <= 255
54 "st.as sp, [%3, %1] \n\t"
55 #else
56 /*
57 * Workaround for NR_CPUS=4k
58 * %1 is bigger than 255 (S9 offset for st.as)
59 */
60 "add2 r24, %3, %1 \n\t"
61 "st sp, [r24] \n\t"
62 #endif
63
64 /*
65 * setup _current_task with incoming tsk.
66 * optionally, set r25 to that as well
67 * For SMP extra work to get to &_current_task[cpu]
68 * (open coded SET_CURR_TASK_ON_CPU)
69 */
70 #ifndef CONFIG_SMP
71 "st %2, [@_current_task] \n\t"
72 #else
73 #ifdef CONFIG_ARC_PLAT_EZNPS
74 "lr r24, [%4] \n\t"
75 #ifndef CONFIG_EZNPS_MTM_EXT
76 "lsr r24, r24, 4 \n\t"
77 #endif
78 #else
79 "lr r24, [identity] \n\t"
80 "lsr r24, r24, 8 \n\t"
81 "bmsk r24, r24, 7 \n\t"
82 #endif
83 "add2 r24, @_current_task, r24 \n\t"
84 "st %2, [r24] \n\t"
85 #endif
86 #ifdef CONFIG_ARC_CURR_IN_REG
87 "mov r25, %2 \n\t"
88 #endif
89
90 /* get ksp of incoming task from tsk->thread.ksp */
91 "ld.as sp, [%2, %1] \n\t"
92
93 /* start loading it's CALLEE reg file */
94
95 #ifndef CONFIG_ARC_CURR_IN_REG
96 "ld.ab r25, [sp, 4] \n\t"
97 #else
98 "add sp, sp, 4 \n\t"
99 #endif
100 "ld.ab r24, [sp, 4] \n\t"
101 "ld.ab r23, [sp, 4] \n\t"
102 "ld.ab r22, [sp, 4] \n\t"
103 "ld.ab r21, [sp, 4] \n\t"
104 "ld.ab r20, [sp, 4] \n\t"
105 "ld.ab r19, [sp, 4] \n\t"
106 "ld.ab r18, [sp, 4] \n\t"
107 "ld.ab r17, [sp, 4] \n\t"
108 "ld.ab r16, [sp, 4] \n\t"
109 "ld.ab r15, [sp, 4] \n\t"
110 "ld.ab r14, [sp, 4] \n\t"
111 "ld.ab r13, [sp, 4] \n\t"
112
113 /* last (ret value) = prev : although for ARC it mov r0, r0 */
114 "mov %0, %3 \n\t"
115
116 /* FP/BLINK restore generated by gcc (standard func epilogue */
117
118 : "=r"(tmp)
119 : "n"(KSP_WORD_OFF), "r"(next), "r"(prev)
120 #ifdef CONFIG_ARC_PLAT_EZNPS
121 , "i"(CTOP_AUX_LOGIC_GLOBAL_ID)
122 #endif
123 : "blink"
124 );
125
126 return (struct task_struct *)tmp;
127 }
128