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

Alexey Brodkin
2016-11-04T17:58:17Z

Hi Vineet,

> -----Original Message-----
> From: Vineet Gupta [mailto:vgupta@synopsys.com]
> Sent: Friday, November 04, 2016 12:32 AM
> To: Daniel Lezcano <daniel.lezcano@linaro.org>
> Cc: Noam Camus <noamca@mellanox.com>; tglx@linutronix.de; linux-snps-arc@lists.infradead.org; linux-kernel@vger.kernel.org;
> Alexey.Brodkin@synopsys.com; Vineet Gupta <vgupta@synopsys.com>; stable@vger.kernel.org
> Subject: [PATCH v2 01/10] ARC: timer: rtc: implement read loop in "C" vs. inline asm
>
> The current code doesn't even compile ....
>
> 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)));

I think original Daniel's comment was about constant value used here.
Now with "_BITUL" it already looks much better but IMHO it would be even better if
31 gets converted here to something like:
------------------------>8--------------------
#define RTC_CTRL_A1_OFFSET 31
------------------------>8--------------------

-Alexey