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/*
* 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;
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;
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)
{
#ifndef CONFIG_SMP
/* PGD cached in MMU reg to avoid 3 mem lookups: task->mm->pgd */
write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd);
#endif
/*
* 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)
{
#ifndef CONFIG_SMP
write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd);
#endif
/* Unconditionally get a new ASID */
get_new_mmu_context(next);
}
#define enter_lazy_tlb(mm, tsk)
#endif /* __ASM_ARC_MMU_CONTEXT_H */
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