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 <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 */