From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from foss.arm.com ([217.140.101.70]:60569 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751202AbcGYJC6 (ORCPT ); Mon, 25 Jul 2016 05:02:58 -0400 Date: Mon, 25 Jul 2016 10:02:59 +0100 From: Will Deacon To: fu.wei@linaro.org Cc: rjw@rjwysocki.net, lenb@kernel.org, daniel.lezcano@linaro.org, tglx@linutronix.de, marc.zyngier@arm.com, lorenzo.pieralisi@arm.com, sudeep.holla@arm.com, hanjun.guo@linaro.org, linux-arm-kernel@lists.infradead.org, linaro-acpi@lists.linaro.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, rruigrok@codeaurora.org, harba@codeaurora.org, cov@codeaurora.org, timur@codeaurora.org, graeme.gregory@linaro.org, al.stone@linaro.org, jcm@redhat.com, wei@redhat.com, arnd@arndb.de, wim@iguana.be, catalin.marinas@arm.com, Suravee.Suthikulpanit@amd.com, leo.duran@amd.com, linux@roeck-us.net, linux-watchdog@vger.kernel.org Subject: Re: [PATCH v8 4/9] clocksource/drivers/arm_arch_timer: use readq to get 64-bit CNTVCT Message-ID: <20160725090258.GA15864@arm.com> References: <1468952284-28942-1-git-send-email-fu.wei@linaro.org> <1468952284-28942-5-git-send-email-fu.wei@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1468952284-28942-5-git-send-email-fu.wei@linaro.org> Sender: linux-watchdog-owner@vger.kernel.org List-Id: linux-watchdog@vger.kernel.org On Wed, Jul 20, 2016 at 02:17:59AM +0800, fu.wei@linaro.org wrote: > From: Fu Wei > > This patch simplify arch_counter_get_cntvct_mem function by > using readq to get 64-bit CNTVCT value instead of readl_relaxed. > > Signed-off-by: Fu Wei > --- > drivers/clocksource/arm_arch_timer.c | 10 +--------- > 1 file changed, 1 insertion(+), 9 deletions(-) > > diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c > index e6fd42d..483d2f9 100644 > --- a/drivers/clocksource/arm_arch_timer.c > +++ b/drivers/clocksource/arm_arch_timer.c > @@ -418,15 +418,7 @@ u32 arch_timer_get_rate(void) > > static u64 arch_counter_get_cntvct_mem(void) > { > - u32 vct_lo, vct_hi, tmp_hi; > - > - do { > - vct_hi = readl_relaxed(arch_counter_base + CNTVCT_HI); > - vct_lo = readl_relaxed(arch_counter_base + CNTVCT_LO); > - tmp_hi = readl_relaxed(arch_counter_base + CNTVCT_HI); > - } while (vct_hi != tmp_hi); > - > - return ((u64) vct_hi << 32) | vct_lo; > + return readq(arch_counter_base + CNTVCT_LO); What's the benefit of doing this? If you use readq here, how can we guarantee that (a) the endpoint won't generate a SLVERR or similar and (b) that we get an atomic read? "If it ain't broke, don't fix it" Will