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 <linux/mm_types.h>
16 #include <linux/sched.h>
17 
18 #include <asm/bitops.h>
19 #include <asm/mmu.h>
20 #include <asm-generic/mm_hooks.h>
21 
22 # ifdef __KERNEL__
23 /*
24  * This function defines the mapping from contexts to VSIDs (virtual
25  * segment IDs).  We use a skew on both the context and the high 4 bits
26  * of the 32-bit virtual address (the "effective segment ID") in order
27  * to spread out the entries in the MMU hash table.
28  */
29 # define CTX_TO_VSID(ctx, va)	(((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
30 				 & 0xffffff)
31 
32 /*
33    MicroBlaze has 256 contexts, so we can just rotate through these
34    as a way of "switching" contexts.  If the TID of the TLB is zero,
35    the PID/TID comparison is disabled, so we can use a TID of zero
36    to represent all kernel pages as shared among all contexts.
37  */
38 
39 static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
40 {
41 }
42 
43 # define NO_CONTEXT	256
44 # define LAST_CONTEXT	255
45 # define FIRST_CONTEXT	1
46 
47 /*
48  * Set the current MMU context.
49  * This is done byloading up the segment registers for the user part of the
50  * address space.
51  *
52  * Since the PGD is immediately available, it is much faster to simply
53  * pass this along as a second parameter, which is required for 8xx and
54  * can be used for debugging on all processors (if you happen to have
55  * an Abatron).
56  */
57 extern void set_context(mm_context_t context, pgd_t *pgd);
58 
59 /*
60  * Bitmap of contexts in use.
61  * The size of this bitmap is LAST_CONTEXT + 1 bits.
62  */
63 extern unsigned long context_map[];
64 
65 /*
66  * This caches the next context number that we expect to be free.
67  * Its use is an optimization only, we can't rely on this context
68  * number to be free, but it usually will be.
69  */
70 extern mm_context_t next_mmu_context;
71 
72 /*
73  * Since we don't have sufficient contexts to give one to every task
74  * that could be in the system, we need to be able to steal contexts.
75  * These variables support that.
76  */
77 extern atomic_t nr_free_contexts;
78 extern struct mm_struct *context_mm[LAST_CONTEXT+1];
79 extern void steal_context(void);
80 
81 /*
82  * Get a new mmu context for the address space described by `mm'.
83  */
84 static inline void get_mmu_context(struct mm_struct *mm)
85 {
86 	mm_context_t ctx;
87 
88 	if (mm->context != NO_CONTEXT)
89 		return;
90 	while (atomic_dec_if_positive(&nr_free_contexts) < 0)
91 		steal_context();
92 	ctx = next_mmu_context;
93 	while (test_and_set_bit(ctx, context_map)) {
94 		ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
95 		if (ctx > LAST_CONTEXT)
96 			ctx = 0;
97 	}
98 	next_mmu_context = (ctx + 1) & LAST_CONTEXT;
99 	mm->context = ctx;
100 	context_mm[ctx] = mm;
101 }
102 
103 /*
104  * Set up the context for a new address space.
105  */
106 # define init_new_context(tsk, mm)	(((mm)->context = NO_CONTEXT), 0)
107 
108 /*
109  * We're finished using the context for an address space.
110  */
111 static inline void destroy_context(struct mm_struct *mm)
112 {
113 	if (mm->context != NO_CONTEXT) {
114 		clear_bit(mm->context, context_map);
115 		mm->context = NO_CONTEXT;
116 		atomic_inc(&nr_free_contexts);
117 	}
118 }
119 
120 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
121 			     struct task_struct *tsk)
122 {
123 	tsk->thread.pgdir = next->pgd;
124 	get_mmu_context(next);
125 	set_context(next->context, next->pgd);
126 }
127 
128 /*
129  * After we have set current->mm to a new value, this activates
130  * the context for the new mm so we see the new mappings.
131  */
132 static inline void activate_mm(struct mm_struct *active_mm,
133 			struct mm_struct *mm)
134 {
135 	current->thread.pgdir = mm->pgd;
136 	get_mmu_context(mm);
137 	set_context(mm->context, mm->pgd);
138 }
139 
140 extern void mmu_context_init(void);
141 
142 # endif /* __KERNEL__ */
143 #endif /* _ASM_MICROBLAZE_MMU_CONTEXT_H */
144