Re: [PATCH v2 02/15] clocksource: orion: Use atomic access for shared registers

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On 01/21/2014 10:12 AM, Ezequiel Garcia wrote:
Replace the driver-specific thread-safe shared register API
by the recently introduced atomic_io_clear_set().

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@xxxxxxxxxxxxxxxxxx>

Hi Ezequiel,

in the future, put me in Cc when modifying files in clocksource that will make my life easier to track the changes.

Thanks.
  -- Daniel

---
  drivers/clocksource/time-orion.c | 28 ++++++++++------------------
  1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/drivers/clocksource/time-orion.c b/drivers/clocksource/time-orion.c
index 9c7f018..3f14e56 100644
--- a/drivers/clocksource/time-orion.c
+++ b/drivers/clocksource/time-orion.c
@@ -35,20 +35,6 @@
  #define ORION_ONESHOT_MAX	0xfffffffe

  static void __iomem *timer_base;
-static DEFINE_SPINLOCK(timer_ctrl_lock);
-
-/*
- * Thread-safe access to TIMER_CTRL register
- * (shared with watchdog timer)
- */
-void orion_timer_ctrl_clrset(u32 clr, u32 set)
-{
-	spin_lock(&timer_ctrl_lock);
-	writel((readl(timer_base + TIMER_CTRL) & ~clr) | set,
-		timer_base + TIMER_CTRL);
-	spin_unlock(&timer_ctrl_lock);
-}
-EXPORT_SYMBOL(orion_timer_ctrl_clrset);
  /*
   * Free-running clocksource handling.
@@ -68,7 +54,8 @@ static int orion_clkevt_next_event(unsigned long delta,
  {
  	/* setup and enable one-shot timer */
  	writel(delta, timer_base + TIMER1_VAL);
-	orion_timer_ctrl_clrset(TIMER1_RELOAD_EN, TIMER1_EN);
+	atomic_io_modify(timer_base + TIMER_CTRL,
+		TIMER1_RELOAD_EN | TIMER1_EN, TIMER1_EN);

I am not convinced this change is worth.

Could you elaborate the race the spinlock should prevent ?


  	return 0;
  }
@@ -80,10 +67,13 @@ static void orion_clkevt_mode(enum clock_event_mode mode,
  		/* setup and enable periodic timer at 1/HZ intervals */
  		writel(ticks_per_jiffy - 1, timer_base + TIMER1_RELOAD);
  		writel(ticks_per_jiffy - 1, timer_base + TIMER1_VAL);
-		orion_timer_ctrl_clrset(0, TIMER1_RELOAD_EN | TIMER1_EN);
+		atomic_io_modify(timer_base + TIMER_CTRL,
+			TIMER1_RELOAD_EN | TIMER1_EN,
+			TIMER1_RELOAD_EN | TIMER1_EN);
  	} else {
  		/* disable timer */
-		orion_timer_ctrl_clrset(TIMER1_RELOAD_EN | TIMER1_EN, 0);
+		atomic_io_modify(timer_base + TIMER_CTRL,
+			TIMER1_RELOAD_EN | TIMER1_EN, 0);
  	}
  }

@@ -131,7 +121,9 @@ static void __init orion_timer_init(struct device_node *np)
  	/* setup timer0 as free-running clocksource */
  	writel(~0, timer_base + TIMER0_VAL);
  	writel(~0, timer_base + TIMER0_RELOAD);
-	orion_timer_ctrl_clrset(0, TIMER0_RELOAD_EN | TIMER0_EN);
+	atomic_io_modify(timer_base + TIMER_CTRL,
+		TIMER0_RELOAD_EN | TIMER0_EN,
+		TIMER0_RELOAD_EN | TIMER0_EN);
  	clocksource_mmio_init(timer_base + TIMER0_VAL, "orion_clocksource",
  			      clk_get_rate(clk), 300, 32,
  			      clocksource_mmio_readl_down);



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