1/*
2 * This file contains the routines for handling the MMU on those
3 * PowerPC implementations where the MMU substantially follows the
4 * architecture specification.  This includes the 6xx, 7xx, 7xxx,
5 * 8260, and POWER3 implementations but excludes the 8xx and 4xx.
6 *  -- paulus
7 *
8 *  Derived from arch/ppc/mm/init.c:
9 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
10 *
11 *  Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
12 *  and Cort Dougan (PReP) (cort@cs.nmt.edu)
13 *    Copyright (C) 1996 Paul Mackerras
14 *  Amiga/APUS changes by Jesper Skov (jskov@cygnus.co.uk).
15 *
16 *  Derived from "arch/i386/mm/init.c"
17 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
18 *
19 *  This program is free software; you can redistribute it and/or
20 *  modify it under the terms of the GNU General Public License
21 *  as published by the Free Software Foundation; either version
22 *  2 of the License, or (at your option) any later version.
23 *
24 */
25
26#include <linux/mm.h>
27#include <linux/init.h>
28
29#include <asm/mmu_context.h>
30#include <asm/tlbflush.h>
31
32unsigned long next_mmu_context;
33unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
34#ifdef FEW_CONTEXTS
35atomic_t nr_free_contexts;
36struct mm_struct *context_mm[LAST_CONTEXT+1];
37void steal_context(void);
38#endif /* FEW_CONTEXTS */
39
40/*
41 * Initialize the context management stuff.
42 */
43void __init
44mmu_context_init(void)
45{
46	/*
47	 * Some processors have too few contexts to reserve one for
48	 * init_mm, and require using context 0 for a normal task.
49	 * Other processors reserve the use of context zero for the kernel.
50	 * This code assumes FIRST_CONTEXT < 32.
51	 */
52	context_map[0] = (1 << FIRST_CONTEXT) - 1;
53	next_mmu_context = FIRST_CONTEXT;
54#ifdef FEW_CONTEXTS
55	atomic_set(&nr_free_contexts, LAST_CONTEXT - FIRST_CONTEXT + 1);
56#endif /* FEW_CONTEXTS */
57}
58
59#ifdef FEW_CONTEXTS
60/*
61 * Steal a context from a task that has one at the moment.
62 * This is only used on 8xx and 4xx and we presently assume that
63 * they don't do SMP.  If they do then this will have to check
64 * whether the MM we steal is in use.
65 * We also assume that this is only used on systems that don't
66 * use an MMU hash table - this is true for 8xx and 4xx.
67 * This isn't an LRU system, it just frees up each context in
68 * turn (sort-of pseudo-random replacement :).  This would be the
69 * place to implement an LRU scheme if anyone was motivated to do it.
70 *  -- paulus
71 */
72void
73steal_context(void)
74{
75	struct mm_struct *mm;
76
77	/* free up context `next_mmu_context' */
78	/* if we shouldn't free context 0, don't... */
79	if (next_mmu_context < FIRST_CONTEXT)
80		next_mmu_context = FIRST_CONTEXT;
81	mm = context_mm[next_mmu_context];
82	flush_tlb_mm(mm);
83	destroy_context(mm);
84}
85#endif /* FEW_CONTEXTS */
86