linux-kernel - Re: [PATCH v9 4/9] clocksource/drivers/arm_arch

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Date:	Mon, 25 Jul 2016 10:50:29 -0500
From:	Timur Tabi <timur@...eaurora.org>
To:	Will Deacon <will.deacon@....com>, fu.wei@...aro.org
Cc:	rjw@...ysocki.net, lenb@...nel.org, daniel.lezcano@...aro.org,
	tglx@...utronix.de, marc.zyngier@....com,
	lorenzo.pieralisi@....com, sudeep.holla@....com,
	hanjun.guo@...aro.org, linux-arm-kernel@...ts.infradead.org,
	linaro-acpi@...ts.linaro.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, rruigrok@...eaurora.org,
	harba@...eaurora.org, cov@...eaurora.org,
	graeme.gregory@...aro.org, al.stone@...aro.org, jcm@...hat.com,
	wei@...hat.com, arnd@...db.de, wim@...ana.be,
	catalin.marinas@....com, Suravee.Suthikulpanit@....com,
	leo.duran@....com, linux@...ck-us.net,
	linux-watchdog@...r.kernel.org
Subject: Re: [PATCH v9 4/9] clocksource/drivers/arm_arch_timer: use readq to
 get 64-bit CNTVCT

Will Deacon wrote:
>> >  {
>> >-	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);
> Please drop this patch. It doesn't work.

On systems where readq() does work, wouldn't it be more optimal than the 
above while-loop?

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