arch/microblaze/include/asm/mmu_context_mm.h

   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 */