1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3 * Context switch support for Hexagon
4 *
5 * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
6 */
7
8 #include <asm/asm-offsets.h>
9
10 .text
11
12 /*
13 * The register used as a fast-path thread information pointer
14 * is determined as a kernel configuration option. If it happens
15 * to be a callee-save register, we're going to be saving and
16 * restoring it twice here.
17 *
18 * This code anticipates a revised ABI where R20-23 are added
19 * to the set of callee-save registers, but this should be
20 * backward compatible to legacy tools.
21 */
22
23
24 /*
25 * void switch_to(struct task_struct *prev,
26 * struct task_struct *next, struct task_struct *last);
27 */
28 .p2align 2
29 .globl __switch_to
30 .type __switch_to, @function
31
32 /*
33 * When we exit the wormhole, we need to store the previous task
34 * in the new R0's pointer. Technically it should be R2, but they should
35 * be the same; seems like a legacy thing. In short, don't butcher
36 * R0, let it go back out unmolested.
37 */
38
39 __switch_to:
40 /*
41 * Push callee-saves onto "prev" stack.
42 * Here, we're sneaky because the LR and FP
43 * storage of the thread_stack structure
44 * is automagically allocated by allocframe,
45 * so we pass struct size less 8.
46 */
47 allocframe(#(_SWITCH_STACK_SIZE - 8));
48 memd(R29+#(_SWITCH_R2726))=R27:26;
49 memd(R29+#(_SWITCH_R2524))=R25:24;
50 memd(R29+#(_SWITCH_R2322))=R23:22;
51 memd(R29+#(_SWITCH_R2120))=R21:20;
52 memd(R29+#(_SWITCH_R1918))=R19:18;
53 memd(R29+#(_SWITCH_R1716))=R17:16;
54 /* Stash thread_info pointer in task_struct */
55 memw(R0+#_TASK_THREAD_INFO) = THREADINFO_REG;
56 memw(R0 +#(_TASK_STRUCT_THREAD + _THREAD_STRUCT_SWITCH_SP)) = R29;
57 /* Switch to "next" stack and restore callee saves from there */
58 R29 = memw(R1 + #(_TASK_STRUCT_THREAD + _THREAD_STRUCT_SWITCH_SP));
59 {
60 R27:26 = memd(R29+#(_SWITCH_R2726));
61 R25:24 = memd(R29+#(_SWITCH_R2524));
62 }
63 {
64 R23:22 = memd(R29+#(_SWITCH_R2322));
65 R21:20 = memd(R29+#(_SWITCH_R2120));
66 }
67 {
68 R19:18 = memd(R29+#(_SWITCH_R1918));
69 R17:16 = memd(R29+#(_SWITCH_R1716));
70 }
71 {
72 /* THREADINFO_REG is currently one of the callee-saved regs
73 * above, and so be sure to re-load it last.
74 */
75 THREADINFO_REG = memw(R1 + #_TASK_THREAD_INFO);
76 R31:30 = memd(R29+#_SWITCH_FP);
77 }
78 {
79 R29 = add(R29,#_SWITCH_STACK_SIZE);
80 jumpr R31;
81 }
82 .size __switch_to, .-__switch_to