/* mmu-context.c: MMU context allocation and management
   *
   * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
   * Written by David Howells (dhowells@redhat.com)
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   */
  
  #include <linux/sched.h>
  #include <linux/mm.h>
  #include <asm/tlbflush.h>
  
  #define NR_CXN	4096
  
  static unsigned long cxn_bitmap[NR_CXN / (sizeof(unsigned long) * 8)];
  static LIST_HEAD(cxn_owners_lru);
  static DEFINE_SPINLOCK(cxn_owners_lock);
  
  int __nongpreldata cxn_pinned = -1;
  
  
  /*****************************************************************************/
  /*
   * initialise a new context
   */
  int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
  {
  	memset(&mm->context, 0, sizeof(mm->context));
  	INIT_LIST_HEAD(&mm->context.id_link);
  	mm->context.itlb_cached_pge = 0xffffffffUL;
  	mm->context.dtlb_cached_pge = 0xffffffffUL;
  
  	return 0;
  } /* end init_new_context() */
  
  /*****************************************************************************/
  /*
   * make sure a kernel MMU context has a CPU context number
   * - call with cxn_owners_lock held
   */
  static unsigned get_cxn(mm_context_t *ctx)
  {
  	struct list_head *_p;
  	mm_context_t *p;
  	unsigned cxn;
  
  	if (!list_empty(&ctx->id_link)) {
  		list_move_tail(&ctx->id_link, &cxn_owners_lru);
  	}
  	else {
  		/* find the first unallocated context number
  		 * - 0 is reserved for the kernel
  		 */
  		cxn = find_next_zero_bit(cxn_bitmap, NR_CXN, 1);
  		if (cxn < NR_CXN) {
  			set_bit(cxn, cxn_bitmap);
  		}
  		else {
  			/* none remaining - need to steal someone else's cxn */
  			p = NULL;
  			list_for_each(_p, &cxn_owners_lru) {
  				p = list_entry(_p, mm_context_t, id_link);
  				if (!p->id_busy && p->id != cxn_pinned)
  					break;
  			}
  
  			BUG_ON(_p == &cxn_owners_lru);
  
  			cxn = p->id;
  			p->id = 0;
  			list_del_init(&p->id_link);
  			__flush_tlb_mm(cxn);
  		}
  
  		ctx->id = cxn;
  		list_add_tail(&ctx->id_link, &cxn_owners_lru);
  	}
  
  	return ctx->id;
  } /* end get_cxn() */
  
  /*****************************************************************************/
  /*
   * restore the current TLB miss handler mapped page tables into the MMU context and set up a
   * mapping for the page directory
   */
  void change_mm_context(mm_context_t *old, mm_context_t *ctx, pgd_t *pgd)
  {
  	unsigned long _pgd;
  
  	_pgd = virt_to_phys(pgd);
  
  	/* save the state of the outgoing MMU context */
  	old->id_busy = 0;
  
  	asm volatile("movsg scr0,%0"   : "=r"(old->itlb_cached_pge));
  	asm volatile("movsg dampr4,%0" : "=r"(old->itlb_ptd_mapping));
  	asm volatile("movsg scr1,%0"   : "=r"(old->dtlb_cached_pge));
  	asm volatile("movsg dampr5,%0" : "=r"(old->dtlb_ptd_mapping));
  
  	/* select an MMU context number */
  	spin_lock(&cxn_owners_lock);
  	get_cxn(ctx);
  	ctx->id_busy = 1;
  	spin_unlock(&cxn_owners_lock);
  
  	asm volatile("movgs %0,cxnr"   : : "r"(ctx->id));
  
  	/* restore the state of the incoming MMU context */
  	asm volatile("movgs %0,scr0"   : : "r"(ctx->itlb_cached_pge));
  	asm volatile("movgs %0,dampr4" : : "r"(ctx->itlb_ptd_mapping));
  	asm volatile("movgs %0,scr1"   : : "r"(ctx->dtlb_cached_pge));
  	asm volatile("movgs %0,dampr5" : : "r"(ctx->dtlb_ptd_mapping));
  
  	/* map the PGD into uncached virtual memory */
  	asm volatile("movgs %0,ttbr"   : : "r"(_pgd));
  	asm volatile("movgs %0,dampr3"
  		     :: "r"(_pgd | xAMPRx_L | xAMPRx_M | xAMPRx_SS_16Kb |
  			    xAMPRx_S | xAMPRx_C | xAMPRx_V));
  
  } /* end change_mm_context() */
  
  /*****************************************************************************/
  /*
   * finished with an MMU context number
   */
  void destroy_context(struct mm_struct *mm)
  {
  	mm_context_t *ctx = &mm->context;
  
  	spin_lock(&cxn_owners_lock);
  
  	if (!list_empty(&ctx->id_link)) {
  		if (ctx->id == cxn_pinned)
  			cxn_pinned = -1;
  
  		list_del_init(&ctx->id_link);
  		clear_bit(ctx->id, cxn_bitmap);
  		__flush_tlb_mm(ctx->id);
  		ctx->id = 0;
  	}
  
  	spin_unlock(&cxn_owners_lock);
  } /* end destroy_context() */
  
  /*****************************************************************************/
  /*
   * display the MMU context currently a process is currently using
   */
  #ifdef CONFIG_PROC_FS
  char *proc_pid_status_frv_cxnr(struct mm_struct *mm, char *buffer)
  {
  	spin_lock(&cxn_owners_lock);
  	buffer += sprintf(buffer, "CXNR: %u
  ", mm->context.id);
  	spin_unlock(&cxn_owners_lock);
  
  	return buffer;
  } /* end proc_pid_status_frv_cxnr() */
  #endif
  
  /*****************************************************************************/
  /*
   * (un)pin a process's mm_struct's MMU context ID
   */
  int cxn_pin_by_pid(pid_t pid)
  {
  	struct task_struct *tsk;
  	struct mm_struct *mm = NULL;
  	int ret;
  
  	/* unpin if pid is zero */
  	if (pid == 0) {
  		cxn_pinned = -1;
  		return 0;
  	}
  
  	ret = -ESRCH;
  
  	/* get a handle on the mm_struct */
  	read_lock(&tasklist_lock);
  	tsk = find_task_by_vpid(pid);
  	if (tsk) {
  		ret = -EINVAL;
  
  		task_lock(tsk);
  		if (tsk->mm) {
  			mm = tsk->mm;
  			atomic_inc(&mm->mm_users);
  			ret = 0;
  		}
  		task_unlock(tsk);
  	}
  	read_unlock(&tasklist_lock);
  
  	if (ret < 0)
  		return ret;
  
  	/* make sure it has a CXN and pin it */
  	spin_lock(&cxn_owners_lock);
  	cxn_pinned = get_cxn(&mm->context);
  	spin_unlock(&cxn_owners_lock);
  
  	mmput(mm);
  	return 0;
  } /* end cxn_pin_by_pid() */