Re: [PATCH v2 01/10] ARC: timer: rtc: implement read loop in "C" vs. inline asm

Vineet Gupta
2016-11-03T22:23:26Z

On 11/03/2016 02:52 PM, Daniel Lezcano wrote:
> On Thu, Nov 03, 2016 at 02:31:32PM -0700, Vineet Gupta wrote:
>> The current code doesn't even compile ....
>
> Give a better description in the log, especially if this patch is supposed to
> go to stable@

OK.

>
>> CC: stable@vger.kernel.org
>> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
>> ---
>> arch/arc/kernel/time.c | 19 +++++++++++--------
>> 1 file changed, 11 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/arc/kernel/time.c b/arch/arc/kernel/time.c
>> index f927b8dc6edd..1a117b999c0c 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)));
>
> Is the condition correct ? If I refer to your previous answer, the bit will be
> set for status if the counter wrapped up. So in this case, we won't exit the
> loop until we wrap up, no ?

No thats not what I meant. Bit being set there means things are fine (no interrupt
taken, no increment of high after low was readetc). All I changed here was use of
0x8000_0000 to the macro. BBIT0 in assembler means branch if bit was clear.

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