Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759454AbcKCRqb (ORCPT ); Thu, 3 Nov 2016 13:46:31 -0400 Received: from smtprelay.synopsys.com ([198.182.60.111]:57132 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754788AbcKCRqa (ORCPT ); Thu, 3 Nov 2016 13:46:30 -0400 Subject: Re: [PATCH 2/9] ARC: timer: rtc: implement read loop in "C" vs. inline asm To: Daniel Lezcano References: <35bde193-8492-83e0-fb03-8385d8afd007@synopsys.com> <1477954096-770-1-git-send-email-vgupta@synopsys.com> <1477954096-770-3-git-send-email-vgupta@synopsys.com> <20161103170256.GC1859@mai> CC: Noam Camus , , , , Newsgroups: gmane.linux.kernel.arc,gmane.linux.kernel From: Vineet Gupta Message-ID: <534582dc-049b-a4ce-5f88-68838cb7941a@synopsys.com> Date: Thu, 3 Nov 2016 10:45:08 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20161103170256.GC1859@mai> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.10.161.44] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1395 Lines: 48 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 >> --- >> 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 >>