vm_switch.S revision e49ee2906c94cd6a339b2012c23e39d1a39f79e3 
1/*
2 * Context switch support for Hexagon
3 *
4 * Copyright (c) 2010-2011, Code Aurora Forum. All rights reserved.
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License version 2 and
8 * only version 2 as published by the Free Software Foundation.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13 * GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
18 * 02110-1301, USA.
19 */
20
21#include <asm/asm-offsets.h>
22
23.text
24
25/*
26 * The register used as a fast-path thread information pointer
27 * is determined as a kernel configuration option.  If it happens
28 * to be a callee-save register, we're going to be saving and
29 * restoring it twice here.
30 *
31 * This code anticipates a revised ABI where R20-23 are added
32 * to the set of callee-save registers, but this should be
33 * backward compatible to legacy tools.
34 */
35
36
37/*
38 *	void switch_to(struct task_struct *prev,
39 *		struct task_struct *next, struct task_struct *last);
40 */
41	.p2align 2
42	.globl __switch_to
43	.type	__switch_to, @function
44
45/*
46 * When we exit the wormhole, we need to store the previous task
47 * in the new R0's pointer.  Technically it should be R2, but they should
48 * be the same; seems like a legacy thing.  In short, don't butcher
49 * R0, let it go back out unmolested.
50 */
51
52__switch_to:
53	/*
54	 * Push callee-saves onto "prev" stack.
55	 * Here, we're sneaky because the LR and FP
56	 * storage of the thread_stack structure
57	 * is automagically allocated by allocframe,
58	 * so we pass struct size less 8.
59	 */
60	allocframe(#(_SWITCH_STACK_SIZE - 8));
61	memd(R29+#(_SWITCH_R2726))=R27:26;
62	memd(R29+#(_SWITCH_R2524))=R25:24;
63	memd(R29+#(_SWITCH_R2322))=R23:22;
64	memd(R29+#(_SWITCH_R2120))=R21:20;
65	memd(R29+#(_SWITCH_R1918))=R19:18;
66	memd(R29+#(_SWITCH_R1716))=R17:16;
67	/* Stash thread_info pointer in task_struct */
68	memw(R0+#_TASK_THREAD_INFO) = THREADINFO_REG;
69	memw(R0 +#(_TASK_STRUCT_THREAD + _THREAD_STRUCT_SWITCH_SP)) = R29;
70	/* Switch to "next" stack and restore callee saves from there */
71	R29 = memw(R1 + #(_TASK_STRUCT_THREAD + _THREAD_STRUCT_SWITCH_SP));
72	{
73	    R27:26 = memd(R29+#(_SWITCH_R2726));
74	    R25:24 = memd(R29+#(_SWITCH_R2524));
75	}
76	{
77	    R23:22 = memd(R29+#(_SWITCH_R2322));
78	    R21:20 = memd(R29+#(_SWITCH_R2120));
79	}
80	{
81	    R19:18 = memd(R29+#(_SWITCH_R1918));
82	    R17:16 = memd(R29+#(_SWITCH_R1716));
83	}
84	{
85	    /* THREADINFO_REG is currently one of the callee-saved regs
86	     * above, and so be sure to re-load it last.
87	     */
88	    THREADINFO_REG = memw(R1 + #_TASK_THREAD_INFO);
89	    R31:30 = memd(R29+#_SWITCH_FP);
90	}
91	{
92	    R29 = add(R29,#_SWITCH_STACK_SIZE);
93	    jumpr R31;
94	}
95	.size	__switch_to, .-__switch_to
96