--- /dev/null
+/*
+ * 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 */
projects / linux-2.6-microblaze.git / commitdiff