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ARC: add/fix some comments in code - no functional change

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Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
This commit is contained in:
Vineet Gupta
2015-08-19 17:23:58 +05:30
parent 6de6066c0d
commit 090749502f
6 changed files with 23 additions and 22 deletions
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22
arch/arc/include/asm/cmpxchg.h
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@@ -110,18 +110,18 @@ static inline unsigned long __xchg(unsigned long val, volatile void *ptr,
sizeof(*(ptr))))
/*
* On ARC700, EX insn is inherently atomic, so by default "vanilla" xchg() need
* not require any locking. However there's a quirk.
* ARC lacks native CMPXCHG, thus emulated (see above), using external locking -
* incidently it "reuses" the same atomic_ops_lock used by atomic APIs.
* Now, llist code uses cmpxchg() and xchg() on same data, so xchg() needs to
* abide by same serializing rules, thus ends up using atomic_ops_lock as well.
* xchg() maps directly to ARC EX instruction which guarantees atomicity.
* However in !LLSC config, it also needs to be use @atomic_ops_lock spinlock
* due to a subtle reason:
* - For !LLSC, cmpxchg() needs to use that lock (see above) and there is lot
* of kernel code which calls xchg()/cmpxchg() on same data (see llist.h)
* Hence xchg() needs to follow same locking rules.
*
* This however is only relevant if SMP and/or ARC lacks LLSC
* if (UP or LLSC)
* xchg doesn't need serialization
* else <==> !(UP or LLSC) <==> (!UP and !LLSC) <==> (SMP and !LLSC)
* xchg needs serialization
* Technically the lock is also needed for UP (boils down to irq save/restore)
* but we can cheat a bit since cmpxchg() atomic_ops_lock() would cause irqs to
* be disabled thus can't possibly be interrpted/preempted/clobbered by xchg()
* Other way around, xchg is one instruction anyways, so can't be interrupted
* as such
*/
#if !defined(CONFIG_ARC_HAS_LLSC) && defined(CONFIG_SMP)

2
arch/arc/include/asm/perf_event.h
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@@ -95,7 +95,7 @@ static const char * const arc_pmu_ev_hw_map[] = {
/* counts condition */
[PERF_COUNT_HW_INSTRUCTIONS] = "iall",
[PERF_COUNT_HW_BRANCH_INSTRUCTIONS] = "ijmp",
[PERF_COUNT_HW_BRANCH_INSTRUCTIONS] = "ijmp", /* Excludes ZOL jumps */
[PERF_COUNT_ARC_BPOK] = "bpok", /* NP-NT, PT-T, PNT-NT */
[PERF_COUNT_HW_BRANCH_MISSES] = "bpfail", /* NP-T, PT-NT, PNT-T */