1/*
2 * MMU context handling.
3 *
4 * Copyright (C) 2011 Tobias Klauser <tklauser@distanz.ch>
5 * Copyright (C) 2009 Wind River Systems Inc
6 * Implemented by fredrik.markstrom@gmail.com and ivarholmqvist@gmail.com
7 *
8 * This file is subject to the terms and conditions of the GNU General Public
9 * License. See the file "COPYING" in the main directory of this archive
10 * for more details.
11 */
12
13#include <linux/mm.h>
14
15#include <asm/cpuinfo.h>
16#include <asm/mmu_context.h>
17#include <asm/tlb.h>
18
19/* The pids position and mask in context */
20#define PID_SHIFT 0
21#define PID_BITS (cpuinfo.tlb_pid_num_bits)
22#define PID_MASK ((1UL << PID_BITS) - 1)
23
24/* The versions position and mask in context */
25#define VERSION_BITS (32 - PID_BITS)
26#define VERSION_SHIFT (PID_SHIFT + PID_BITS)
27#define VERSION_MASK ((1UL << VERSION_BITS) - 1)
28
29/* Return the version part of a context */
30#define CTX_VERSION(c) (((c) >> VERSION_SHIFT) & VERSION_MASK)
31
32/* Return the pid part of a context */
33#define CTX_PID(c) (((c) >> PID_SHIFT) & PID_MASK)
34
35/* Value of the first context (version 1, pid 0) */
36#define FIRST_CTX ((1UL << VERSION_SHIFT) | (0 << PID_SHIFT))
37
38static mm_context_t next_mmu_context;
39
40/*
41 * Initialize MMU context management stuff.
42 */
43void __init mmu_context_init(void)
44{
45 /* We need to set this here because the value depends on runtime data
46 * from cpuinfo */
47 next_mmu_context = FIRST_CTX;
48}
49
50/*
51 * Set new context (pid), keep way
52 */
53static void set_context(mm_context_t context)
54{
55 set_mmu_pid(CTX_PID(context));
56}
57
58static mm_context_t get_new_context(void)
59{
60 /* Return the next pid */
61 next_mmu_context += (1UL << PID_SHIFT);
62
63 /* If the pid field wraps around we increase the version and
64 * flush the tlb */
65 if (unlikely(CTX_PID(next_mmu_context) == 0)) {
66 /* Version is incremented since the pid increment above
67 * overflows info version */
68 flush_cache_all();
69 flush_tlb_all();
70 }
71
72 /* If the version wraps we start over with the first generation, we do
73 * not need to flush the tlb here since it's always done above */
74 if (unlikely(CTX_VERSION(next_mmu_context) == 0))
75 next_mmu_context = FIRST_CTX;
76
77 return next_mmu_context;
78}
79
80void switch_mm(struct mm_struct *prev, struct mm_struct *next,
81 struct task_struct *tsk)
82{
83 unsigned long flags;
84
85 local_irq_save(flags);
86
87 /* If the process context we are swapping in has a different context
88 * generation then we have it should get a new generation/pid */
89 if (unlikely(CTX_VERSION(next->context) !=
90 CTX_VERSION(next_mmu_context)))
91 next->context = get_new_context();
92
93 /* Save the current pgd so the fast tlb handler can find it */
94 pgd_current = next->pgd;
95
96 /* Set the current context */
97 set_context(next->context);
98
99 local_irq_restore(flags);
100}
101
102/*
103 * After we have set current->mm to a new value, this activates
104 * the context for the new mm so we see the new mappings.
105 */
106void activate_mm(struct mm_struct *prev, struct mm_struct *next)
107{
108 next->context = get_new_context();
109 set_context(next->context);
110 pgd_current = next->pgd;
111}
112
113unsigned long get_pid_from_context(mm_context_t *context)
114{
115 return CTX_PID((*context));
116}
117

source code of linux/arch/nios2/mm/mmu_context.c