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