1/*
  2 *  linux/arch/cris/mm/tlb.c
  3 *
  4 *  Copyright (C) 2000, 2001  Axis Communications AB
  5 *  
  6 *  Authors:   Bjorn Wesen (bjornw@axis.com)
  7 *
  8 */
  9
 10#include <linux/init.h>
 11#include <linux/kernel.h>
 12#include <asm/tlb.h>
 13
 14#define D(x)
 15
 16/* The TLB can host up to 64 different mm contexts at the same time.
 17 * The running context is R_MMU_CONTEXT, and each TLB entry contains a
 18 * page_id that has to match to give a hit. In page_id_map, we keep track
 19 * of which mm we have assigned to which page_id, so that we know when
 20 * to invalidate TLB entries.
 21 *
 22 * The last page_id is never running - it is used as an invalid page_id
 23 * so we can make TLB entries that will never match.
 24 *
 25 * Notice that we need to make the flushes atomic, otherwise an interrupt
 26 * handler that uses vmalloced memory might cause a TLB load in the middle
 27 * of a flush causing.
 28 */
 29
 30struct mm_struct *page_id_map[NUM_PAGEID];
 31static int map_replace_ptr = 1;  /* which page_id_map entry to replace next */
 32
 33/* the following functions are similar to those used in the PPC port */
 34
 35static inline void
 36alloc_context(struct mm_struct *mm)
 37{
 38	struct mm_struct *old_mm;
 39
 40	D(printk("tlb: alloc context %d (%p)\n", map_replace_ptr, mm));
 41
 42	/* did we replace an mm ? */
 43
 44	old_mm = page_id_map[map_replace_ptr];
 45
 46	if(old_mm) {
 47		/* throw out any TLB entries belonging to the mm we replace
 48		 * in the map
 49		 */
 50		flush_tlb_mm(old_mm);
 51
 52		old_mm->context.page_id = NO_CONTEXT;
 53	}
 54
 55	/* insert it into the page_id_map */
 56
 57	mm->context.page_id = map_replace_ptr;
 58	page_id_map[map_replace_ptr] = mm;
 59
 60	map_replace_ptr++;
 61
 62	if(map_replace_ptr == INVALID_PAGEID)
 63		map_replace_ptr = 0;         /* wrap around */	
 64}
 65
 66/* 
 67 * if needed, get a new MMU context for the mm. otherwise nothing is done.
 68 */
 69
 70void
 71get_mmu_context(struct mm_struct *mm)
 72{
 73	if(mm->context.page_id == NO_CONTEXT)
 74		alloc_context(mm);
 75}
 76
 77/* called by __exit_mm to destroy the used MMU context if any before
 78 * destroying the mm itself. this is only called when the last user of the mm
 79 * drops it.
 80 *
 81 * the only thing we really need to do here is mark the used PID slot
 82 * as empty.
 83 */
 84
 85void
 86destroy_context(struct mm_struct *mm)
 87{
 88	if(mm->context.page_id != NO_CONTEXT) {
 89		D(printk("destroy_context %d (%p)\n", mm->context.page_id, mm));
 90		flush_tlb_mm(mm);  /* TODO this might be redundant ? */
 91		page_id_map[mm->context.page_id] = NULL;
 92	}
 93}
 94
 95/* called once during VM initialization, from init.c */
 96
 97void __init
 98tlb_init(void)
 99{
100	int i;
101
102	/* clear the page_id map */
103
104	for (i = 1; i < ARRAY_SIZE(page_id_map); i++)
105		page_id_map[i] = NULL;
106	
107	/* invalidate the entire TLB */
108
109	flush_tlb_all();
110
111	/* the init_mm has context 0 from the boot */
112
113	page_id_map[0] = &init_mm;
114}