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
83