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Linux/arch/microblaze/include/asm/mmu_context_mm.h

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  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 

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