1/*
2 * Copyright (C) 2008-2009 Michal Simek <monstr@monstr.eu>
3 * Copyright (C) 2008-2009 PetaLogix
4 * Copyright (C) 2006 Atmark Techno, Inc.
5 *
6 * This file is subject to the terms and conditions of the GNU General Public
7 * License. See the file "COPYING" in the main directory of this archive
8 * for more details.
9 */
10
11#ifndef _ASM_MICROBLAZE_MMU_CONTEXT_H
12#define _ASM_MICROBLAZE_MMU_CONTEXT_H
13
14#include <linux/atomic.h>
15#include <asm/bitops.h>
16#include <asm/mmu.h>
17#include <asm-generic/mm_hooks.h>
18
19# ifdef __KERNEL__
20/*
21 * This function defines the mapping from contexts to VSIDs (virtual
22 * segment IDs).  We use a skew on both the context and the high 4 bits
23 * of the 32-bit virtual address (the "effective segment ID") in order
24 * to spread out the entries in the MMU hash table.
25 */
26# define CTX_TO_VSID(ctx, va)	(((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
27				 & 0xffffff)
28
29/*
30   MicroBlaze has 256 contexts, so we can just rotate through these
31   as a way of "switching" contexts.  If the TID of the TLB is zero,
32   the PID/TID comparison is disabled, so we can use a TID of zero
33   to represent all kernel pages as shared among all contexts.
34 */
35
36static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
37{
38}
39
40# define NO_CONTEXT	256
41# define LAST_CONTEXT	255
42# define FIRST_CONTEXT	1
43
44/*
45 * Set the current MMU context.
46 * This is done byloading up the segment registers for the user part of the
47 * address space.
48 *
49 * Since the PGD is immediately available, it is much faster to simply
50 * pass this along as a second parameter, which is required for 8xx and
51 * can be used for debugging on all processors (if you happen to have
52 * an Abatron).
53 */
54extern void set_context(mm_context_t context, pgd_t *pgd);
55
56/*
57 * Bitmap of contexts in use.
58 * The size of this bitmap is LAST_CONTEXT + 1 bits.
59 */
60extern unsigned long context_map[];
61
62/*
63 * This caches the next context number that we expect to be free.
64 * Its use is an optimization only, we can't rely on this context
65 * number to be free, but it usually will be.
66 */
67extern mm_context_t next_mmu_context;
68
69/*
70 * Since we don't have sufficient contexts to give one to every task
71 * that could be in the system, we need to be able to steal contexts.
72 * These variables support that.
73 */
74extern atomic_t nr_free_contexts;
75extern struct mm_struct *context_mm[LAST_CONTEXT+1];
76extern void steal_context(void);
77
78/*
79 * Get a new mmu context for the address space described by `mm'.
80 */
81static inline void get_mmu_context(struct mm_struct *mm)
82{
83	mm_context_t ctx;
84
85	if (mm->context != NO_CONTEXT)
86		return;
87	while (atomic_dec_if_positive(&nr_free_contexts) < 0)
88		steal_context();
89	ctx = next_mmu_context;
90	while (test_and_set_bit(ctx, context_map)) {
91		ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
92		if (ctx > LAST_CONTEXT)
93			ctx = 0;
94	}
95	next_mmu_context = (ctx + 1) & LAST_CONTEXT;
96	mm->context = ctx;
97	context_mm[ctx] = mm;
98}
99
100/*
101 * Set up the context for a new address space.
102 */
103# define init_new_context(tsk, mm)	(((mm)->context = NO_CONTEXT), 0)
104
105/*
106 * We're finished using the context for an address space.
107 */
108static inline void destroy_context(struct mm_struct *mm)
109{
110	if (mm->context != NO_CONTEXT) {
111		clear_bit(mm->context, context_map);
112		mm->context = NO_CONTEXT;
113		atomic_inc(&nr_free_contexts);
114	}
115}
116
117static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
118			     struct task_struct *tsk)
119{
120	tsk->thread.pgdir = next->pgd;
121	get_mmu_context(next);
122	set_context(next->context, next->pgd);
123}
124
125/*
126 * After we have set current->mm to a new value, this activates
127 * the context for the new mm so we see the new mappings.
128 */
129static inline void activate_mm(struct mm_struct *active_mm,
130			struct mm_struct *mm)
131{
132	current->thread.pgdir = mm->pgd;
133	get_mmu_context(mm);
134	set_context(mm->context, mm->pgd);
135}
136
137extern void mmu_context_init(void);
138
139# endif /* __KERNEL__ */
140#endif /* _ASM_MICROBLAZE_MMU_CONTEXT_H */
141