Re: [PATCH 2/9] ARC: timer: rtc: implement read loop in "C" vs. inline asm

Vineet Gupta
2016-11-03T17:46:31Z

On 11/03/2016 10:02 AM, Daniel Lezcano wrote:
> On Mon, Oct 31, 2016 at 03:48:09PM -0700, Vineet Gupta wrote:
>> To allow for easy movement into drivers/clocksource
>>
>> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
>> ---
>> arch/arc/kernel/time.c | 13 +++++--------
>> 1 file changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/arc/kernel/time.c b/arch/arc/kernel/time.c
>> index a2db010cde18..2c51e3cafad0 100644
>> --- a/arch/arc/kernel/time.c
>> +++ b/arch/arc/kernel/time.c
>> @@ -153,14 +153,11 @@ 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));
>> + 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 & 0x80000000UL));
>
> Replace the literal 0x80000000UL by a macro.

OK !

> What is the 'status' for ?

Hardware keeps a internal state machine for atomic readout of low/high. So if an
interrupt is taken between reading low and high, or if high increments after low
is read, then the bit forces a loop to retry.

>
>> return stamp.full;
>> }
>> --
>> 2.7.4
>>