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Message-ID: <534582dc-049b-a4ce-5f88-68838cb7941a@synopsys.com>
Date: Thu, 3 Nov 2016 10:45:08 -0700
From: Vineet Gupta <Vineet.Gupta1@...opsys.com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
CC: Noam Camus <noamca@...lanox.com>, <tglx@...utronix.de>,
<linux-snps-arc@...ts.infradead.org>,
<Alexey.Brodkin@...opsys.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/9] ARC: timer: rtc: implement read loop in "C" vs.
inline asm
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@...opsys.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
>>
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