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authorVineet Gupta <vgupta@synopsys.com>2015-08-19 14:53:58 +0300
committerVineet Gupta <vgupta@synopsys.com>2015-08-20 16:35:49 +0300
commit090749502ff20d7d9ec244036fe636b6bf0433b6 (patch)
tree52ce66c6c0a525b4a9eff0ee5917c52f72479ead /arch/arc
parent6de6066c0d24a66df465cf87a4041ef7ef35ba6f (diff)
downloadlinux-090749502ff20d7d9ec244036fe636b6bf0433b6.tar.xz
ARC: add/fix some comments in code - no functional change
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Diffstat (limited to 'arch/arc')
-rw-r--r--arch/arc/boot/dts/axc003.dtsi13
-rw-r--r--arch/arc/include/asm/cmpxchg.h22
-rw-r--r--arch/arc/include/asm/perf_event.h2
-rw-r--r--arch/arc/kernel/perf_event.c4
-rw-r--r--arch/arc/kernel/process.c2
-rw-r--r--arch/arc/plat-axs10x/axs10x.c2
6 files changed, 23 insertions, 22 deletions
diff --git a/arch/arc/boot/dts/axc003.dtsi b/arch/arc/boot/dts/axc003.dtsi
index 1cd5e82f5dc2..846481f37eef 100644
--- a/arch/arc/boot/dts/axc003.dtsi
+++ b/arch/arc/boot/dts/axc003.dtsi
@@ -72,12 +72,13 @@
};
/*
- * This INTC is actually connected to DW APB GPIO
- * which acts as a wire between MB INTC and CPU INTC.
- * GPIO INTC is configured in platform init code
- * and here we mimic direct connection from MB INTC to
- * CPU INTC, thus we set "interrupts = <7>" instead of
- * "interrupts = <12>"
+ * The DW APB ICTL intc on MB is connected to CPU intc via a
+ * DT "invisible" DW APB GPIO block, configured to simply pass thru
+ * interrupts - setup accordinly in platform init (plat-axs10x/ax10x.c)
+ *
+ * So here we mimic a direct connection betwen them, ignoring the
+ * ABPG GPIO. Thus set "interrupts = <24>" (DW APB GPIO to core)
+ * instead of "interrupts = <12>" (DW APB ICTL to DW APB GPIO)
*
* This intc actually resides on MB, but we move it here to
* avoid duplicating the MB dtsi file given that IRQ from
diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
index 44fd531f4d7b..af7a2db139c9 100644
--- a/arch/arc/include/asm/cmpxchg.h
+++ b/arch/arc/include/asm/cmpxchg.h
@@ -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)
diff --git a/arch/arc/include/asm/perf_event.h b/arch/arc/include/asm/perf_event.h
index 2b8880e953a2..e2eaf6fb0468 100644
--- a/arch/arc/include/asm/perf_event.h
+++ b/arch/arc/include/asm/perf_event.h
@@ -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 */
diff --git a/arch/arc/kernel/perf_event.c b/arch/arc/kernel/perf_event.c
index 1287388c258a..79ab199a9778 100644
--- a/arch/arc/kernel/perf_event.c
+++ b/arch/arc/kernel/perf_event.c
@@ -199,8 +199,8 @@ static void arc_pmu_start(struct perf_event *event, int flags)
event->hw.state = 0;
/* enable ARC pmu here */
- write_aux_reg(ARC_REG_PCT_INDEX, idx);
- write_aux_reg(ARC_REG_PCT_CONFIG, hwc->config);
+ write_aux_reg(ARC_REG_PCT_INDEX, idx); /* counter # */
+ write_aux_reg(ARC_REG_PCT_CONFIG, hwc->config); /* condition */
}
static void arc_pmu_stop(struct perf_event *event, int flags)
diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index 44092456776f..91d5a0f1f3f7 100644
--- a/arch/arc/kernel/process.c
+++ b/arch/arc/kernel/process.c
@@ -65,7 +65,7 @@ asmlinkage void ret_from_fork(void);
* ------------------
* | r25 | <==== top of Stack (thread.ksp)
* ~ ~
- * | --to-- | (CALLEE Regs of user mode)
+ * | --to-- | (CALLEE Regs of kernel mode)
* | r13 |
* ------------------
* | fp |
diff --git a/arch/arc/plat-axs10x/axs10x.c b/arch/arc/plat-axs10x/axs10x.c
index e7769c3ab5f2..ad9825d4026a 100644
--- a/arch/arc/plat-axs10x/axs10x.c
+++ b/arch/arc/plat-axs10x/axs10x.c
@@ -46,7 +46,7 @@ static void __init axs10x_enable_gpio_intc_wire(void)
* ------------------- -------------------
* | snps,dw-apb-gpio | | snps,dw-apb-gpio |
* ------------------- -------------------
- * | |
+ * | #12 |
* | [ Debug UART on cpu card ]
* |
* ------------------------