ARC: MMU Context Management

#define DC_CTRL_INV_MODE_FLUSH  0x40

#define DC_CTRL_FLUSH_STATUS    0x100

/* MMU Management regs */

#define ARC_REG_PID		0x409

#define ARC_REG_SCRATCH_DATA0	0x418

/* Bits in MMU PID register */

#define MMU_ENABLE		(1 << 31)	/* Enable MMU for process */

/*

 * Floating Pt Registers

 * Status regs are read-only (build-time) so need not be saved/restored

/*

 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 */

#ifndef _ASM_ARC_MMU_H

#define _ASM_ARC_MMU_H

#ifndef __ASSEMBLY__

typedef struct {

	unsigned long asid;	/* Pvt Addr-Space ID for mm */

#ifdef CONFIG_ARC_TLB_DBG

	struct task_struct *tsk;

#endif

} mm_context_t;

#endif

#endif

/*

 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 *

 * vineetg: May 2011

 *  -Refactored get_new_mmu_context( ) to only handle live-mm.

 *   retiring-mm handled in other hooks

 *

 * Vineetg: March 25th, 2008: Bug #92690

 *  -Major rewrite of Core ASID allocation routine get_new_mmu_context

 *

 * Amit Bhor, Sameer Dhavale: Codito Technologies 2004

 */

#ifndef _ASM_ARC_MMU_CONTEXT_H

#define _ASM_ARC_MMU_CONTEXT_H

#include <asm/arcregs.h>

#include <asm/tlb.h>

#include <asm-generic/mm_hooks.h>

/*		ARC700 ASID Management

 *

 * ARC MMU provides 8-bit ASID (0..255) to TAG TLB entries, allowing entries

 * with same vaddr (different tasks) to co-exit. This provides for

 * "Fast Context Switch" i.e. no TLB flush on ctxt-switch

 *

 * Linux assigns each task a unique ASID. A simple round-robin allocation

 * of H/w ASID is done using software tracker @asid_cache.

 * When it reaches max 255, the allocation cycle starts afresh by flushing

 * the entire TLB and wrapping ASID back to zero.

 *

 * For book-keeping, Linux uses a couple of data-structures:

 *  -mm_struct has an @asid field to keep a note of task's ASID (needed at the

 *   time of say switch_mm( )

 *  -An array of mm structs @asid_mm_map[] for asid->mm the reverse mapping,

 *  given an ASID, finding the mm struct associated.

 *

 * The round-robin allocation algorithm allows for ASID stealing.

 * If asid tracker is at "x-1", a new req will allocate "x", even if "x" was

 * already assigned to another (switched-out) task. Obviously the prev owner

 * is marked with an invalid ASID to make it request for a new ASID when it

 * gets scheduled next time. However its TLB entries (with ASID "x") could

 * exist, which must be cleared before the same ASID is used by the new owner.

 * Flushing them would be plausible but costly solution. Instead we force a

 * allocation policy quirk, which ensures that a stolen ASID won't have any

 * TLB entries associates, alleviating the need to flush.

 * The quirk essentially is not allowing ASID allocated in prev cycle

 * to be used past a roll-over in the next cycle.

 * When this happens (i.e. task ASID > asid tracker), task needs to refresh

 * its ASID, aligning it to current value of tracker. If the task doesn't get

 * scheduled past a roll-over, hence its ASID is not yet realigned with

 * tracker, such ASID is anyways safely reusable because it is

 * gauranteed that TLB entries with that ASID wont exist.

 */

#define FIRST_ASID  0

#define MAX_ASID    255			/* 8 bit PID field in PID Aux reg */

#define NO_ASID     (MAX_ASID + 1)	/* ASID Not alloc to mmu ctxt */

#define NUM_ASID    ((MAX_ASID - FIRST_ASID) + 1)

/* ASID to mm struct mapping */

extern struct mm_struct *asid_mm_map[NUM_ASID + 1];

extern int asid_cache;

/*

 * Assign a new ASID to task. If the task already has an ASID, it is

 * relinquished.

 */

static inline void get_new_mmu_context(struct mm_struct *mm)

{

	struct mm_struct *prev_owner;

	unsigned long flags;

	local_irq_save(flags);

	/*

	 * Relinquish the currently owned ASID (if any).

	 * Doing unconditionally saves a cmp-n-branch; for already unused

	 * ASID slot, the value was/remains NULL

	 */

	asid_mm_map[mm->context.asid] = (struct mm_struct *)NULL;

	/* move to new ASID */

	if (++asid_cache > MAX_ASID) {	/* ASID roll-over */

		asid_cache = FIRST_ASID;

		flush_tlb_all();

	}

	/*

	 * Is next ASID already owned by some-one else (we are stealing it).

	 * If so, let the orig owner be aware of this, so when it runs, it

	 * asks for a brand new ASID. This would only happen for a long-lived

	 * task with ASID from prev allocation cycle (before ASID roll-over).

	 *

	 * This might look wrong - if we are re-using some other task's ASID,

	 * won't we use it's stale TLB entries too. Actually switch_mm( ) takes

	 * care of such a case: it ensures that task with ASID from prev alloc

	 * cycle, when scheduled will refresh it's ASID: see switch_mm( ) below

	 * The stealing scenario described here will only happen if that task

	 * didn't get a chance to refresh it's ASID - implying stale entries

	 * won't exist.

	 */

	prev_owner = asid_mm_map[asid_cache];

	if (prev_owner)

		prev_owner->context.asid = NO_ASID;

	/* Assign new ASID to tsk */

	asid_mm_map[asid_cache] = mm;

	mm->context.asid = asid_cache;

#ifdef CONFIG_ARC_TLB_DBG

	pr_info("ARC_TLB_DBG: NewMM=0x%x OldMM=0x%x task_struct=0x%x Task: %s,"

	       " pid:%u, assigned asid:%lu\n",

	       (unsigned int)mm, (unsigned int)prev_owner,

	       (unsigned int)(mm->context.tsk), (mm->context.tsk)->comm,

	       (mm->context.tsk)->pid, mm->context.asid);

#endif

	write_aux_reg(ARC_REG_PID, asid_cache | MMU_ENABLE);

	local_irq_restore(flags);

}

/*

 * Initialize the context related info for a new mm_struct

 * instance.

 */

static inline int

init_new_context(struct task_struct *tsk, struct mm_struct *mm)

{

	mm->context.asid = NO_ASID;

#ifdef CONFIG_ARC_TLB_DBG

	mm->context.tsk = tsk;

#endif

	return 0;

}

/* Prepare the MMU for task: setup PID reg with allocated ASID

    If task doesn't have an ASID (never alloc or stolen, get a new ASID)

*/

static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,

			     struct task_struct *tsk)

{

	/* PGD cached in MMU reg to avoid 3 mem lookups: task->mm->pgd */

	write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd);

	/*

	 * Get a new ASID if task doesn't have a valid one. Possible when

	 *  -task never had an ASID (fresh after fork)

	 *  -it's ASID was stolen - past an ASID roll-over.

	 *  -There's a third obscure scenario (if this task is running for the

	 *   first time afer an ASID rollover), where despite having a valid

	 *   ASID, we force a get for new ASID - see comments at top.

	 *

	 * Both the non-alloc scenario and first-use-after-rollover can be

	 * detected using the single condition below:  NO_ASID = 256

	 * while asid_cache is always a valid ASID value (0-255).

	 */

	if (next->context.asid > asid_cache) {

		get_new_mmu_context(next);

	} else {

		/*

		 * XXX: This will never happen given the chks above

		 * BUG_ON(next->context.asid > MAX_ASID);

		 */

		write_aux_reg(ARC_REG_PID, next->context.asid | MMU_ENABLE);

	}

}

static inline void destroy_context(struct mm_struct *mm)

{

	unsigned long flags;

	local_irq_save(flags);

	asid_mm_map[mm->context.asid] = NULL;

	mm->context.asid = NO_ASID;

	local_irq_restore(flags);

}

/* it seemed that deactivate_mm( ) is a reasonable place to do book-keeping

 * for retiring-mm. However destroy_context( ) still needs to do that because

 * between mm_release( ) = >deactive_mm( ) and

 * mmput => .. => __mmdrop( ) => destroy_context( )

 * there is a good chance that task gets sched-out/in, making it's ASID valid

 * again (this teased me for a whole day).

 */

#define deactivate_mm(tsk, mm)   do { } while (0)

static inline void activate_mm(struct mm_struct *prev, struct mm_struct *next)

{

	write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd);

	/* Unconditionally get a new ASID */

	get_new_mmu_context(next);

}

#define enter_lazy_tlb(mm, tsk)

#endif /* __ASM_ARC_MMU_CONTEXT_H */

/*

 * TLB Management (flush/create/diagnostics) for ARC700

 *

 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License version 2 as

 * published by the Free Software Foundation.

 */

#include <linux/module.h>

#include <asm/arcregs.h>

#include <asm/mmu_context.h>

#include <asm/tlb.h>

/* A copy of the ASID from the PID reg is kept in asid_cache */

int asid_cache = FIRST_ASID;

/* ASID to mm struct mapping. We have one extra entry corresponding to

 * NO_ASID to save us a compare when clearing the mm entry for old asid

 * see get_new_mmu_context (asm-arc/mmu_context.h)

 */

struct mm_struct *asid_mm_map[NUM_ASID + 1];