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 
36 static 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  */
54 extern 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  */
60 extern 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  */
67 extern 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  */
74 extern atomic_t nr_free_contexts;
75 extern struct mm_struct *context_mm[LAST_CONTEXT+1];
76 extern void steal_context(void);
77 
78 /*
79  * Get a new mmu context for the address space described by `mm'.
80  */
81 static 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  */
108 static 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 
117 static 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  */
129 static 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 
137 extern void mmu_context_init(void);
138 
139 # endif /* __KERNEL__ */
140 #endif /* _ASM_MICROBLAZE_MMU_CONTEXT_H */
141