ARC: timer: rtc: implement read loop in "C" vs. inline asm

The current code doesn't even compile as somehow the inline assembly
can't see the register names defined as ARC_RTC_*
I'm pretty sure It worked when I first got it merged, but the tools were
definitely different then.

So better to write this in "C" anyways.

CC: stable@vger.kernel.org	#4.2+
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

1 files changed, 11 insertions, 8 deletions

diff --git a/arch/arc/kernel/time.c b/arch/arc/kernel/time.c
index f927b8dc6edd..c10390d1ddb6 100644
--- a/arch/arc/kernel/time.c
+++ b/arch/arc/kernel/time.c
@@ -152,14 +152,17 @@ static cycle_t arc_read_rtc(struct clocksource *cs)
                 cycle_t  full;
         } stamp;
 
-
-        __asm__ __volatile(
-        "1:                                             \n"
-        "       lr              %0, [AUX_RTC_LOW]       \n"
-        "       lr              %1, [AUX_RTC_HIGH]      \n"
-        "       lr              %2, [AUX_RTC_CTRL]      \n"
-        "       bbit0.nt        %2, 31, 1b              \n"
-        : "=r" (stamp.low), "=r" (stamp.high), "=r" (status));
+        /*
+         * hardware has an internal state machine which tracks readout of
+         * low/high and updates the CTRL.status if
+         *  - interrupt/exception taken between the two reads
+         *  - high increments after low has been read
+         */
+        do {
+                stamp.low = read_aux_reg(AUX_RTC_LOW);
+                stamp.high = read_aux_reg(AUX_RTC_HIGH);
+                status = read_aux_reg(AUX_RTC_CTRL);
+        } while (!(status & _BITUL(31)));
 
         return stamp.full;
 }