1/*
  2 * This file contains the routines for handling the MMU on those
  3 * PowerPC implementations where the MMU substantially follows the
  4 * architecture specification.  This includes the 6xx, 7xx, 7xxx,
  5 * 8260, and POWER3 implementations but excludes the 8xx and 4xx.
  6 *  -- paulus
  7 *
  8 *  Derived from arch/ppc/mm/init.c:
  9 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
 10 *
 11 *  Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
 12 *  and Cort Dougan (PReP) (cort@cs.nmt.edu)
 13 *    Copyright (C) 1996 Paul Mackerras
 14 *
 15 *  Derived from "arch/i386/mm/init.c"
 16 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 17 *
 18 *  This program is free software; you can redistribute it and/or
 19 *  modify it under the terms of the GNU General Public License
 20 *  as published by the Free Software Foundation; either version
 21 *  2 of the License, or (at your option) any later version.
 22 *
 23 */
 24
 25#include <linux/mm.h>
 26#include <linux/init.h>
 27#include <linux/export.h>
 28
 29#include <asm/mmu_context.h>
 30#include <asm/tlbflush.h>
 31
 32/*
 33 * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
 34 * (virtual segment identifiers) for each context.  Although the
 35 * hardware supports 24-bit VSIDs, and thus >1 million contexts,
 36 * we only use 32,768 of them.  That is ample, since there can be
 37 * at most around 30,000 tasks in the system anyway, and it means
 38 * that we can use a bitmap to indicate which contexts are in use.
 39 * Using a bitmap means that we entirely avoid all of the problems
 40 * that we used to have when the context number overflowed,
 41 * particularly on SMP systems.
 42 *  -- paulus.
 43 */
 44#define NO_CONTEXT      	((unsigned long) -1)
 45#define LAST_CONTEXT    	32767
 46#define FIRST_CONTEXT    	1
 47
 48/*
 49 * This function defines the mapping from contexts to VSIDs (virtual
 50 * segment IDs).  We use a skew on both the context and the high 4 bits
 51 * of the 32-bit virtual address (the "effective segment ID") in order
 52 * to spread out the entries in the MMU hash table.  Note, if this
 53 * function is changed then arch/ppc/mm/hashtable.S will have to be
 54 * changed to correspond.
 55 *
 56 *
 57 * CTX_TO_VSID(ctx, va)	(((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
 58 *				 & 0xffffff)
 59 */
 60
 61static unsigned long next_mmu_context;
 62static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
 63
 64unsigned long __init_new_context(void)
 65{
 66	unsigned long ctx = next_mmu_context;
 67
 68	while (test_and_set_bit(ctx, context_map)) {
 69		ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
 70		if (ctx > LAST_CONTEXT)
 71			ctx = 0;
 72	}
 73	next_mmu_context = (ctx + 1) & LAST_CONTEXT;
 74
 75	return ctx;
 76}
 77EXPORT_SYMBOL_GPL(__init_new_context);
 78
 79/*
 80 * Set up the context for a new address space.
 81 */
 82int init_new_context(struct task_struct *t, struct mm_struct *mm)
 83{
 84	mm->context.id = __init_new_context();
 85
 86	return 0;
 87}
 88
 89/*
 90 * Free a context ID. Make sure to call this with preempt disabled!
 91 */
 92void __destroy_context(unsigned long ctx)
 93{
 94	clear_bit(ctx, context_map);
 95}
 96EXPORT_SYMBOL_GPL(__destroy_context);
 97
 98/*
 99 * We're finished using the context for an address space.
100 */
101void destroy_context(struct mm_struct *mm)
102{
103	preempt_disable();
104	if (mm->context.id != NO_CONTEXT) {
105		__destroy_context(mm->context.id);
106		mm->context.id = NO_CONTEXT;
107	}
108	preempt_enable();
109}
110
111/*
112 * Initialize the context management stuff.
113 */
114void __init mmu_context_init(void)
115{
116	/* Reserve context 0 for kernel use */
117	context_map[0] = (1 << FIRST_CONTEXT) - 1;
118	next_mmu_context = FIRST_CONTEXT;
119}