linux-kernel - Re: [PATCH v2 2/2] ARM: perf: Add support for Scorpion PMUs

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Message-ID: <20150227194656.GB24818@arm.com>
Date:	Fri, 27 Feb 2015 19:46:56 +0000
From:	Will Deacon <will.deacon@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Ashwin Chaugule <ashwin.chaugule@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <Mark.Rutland@....com>,
	Neil Leeder <nleeder@...eaurora.org>,
	Ashwin Chaugule <ashwinc@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] ARM: perf: Add support for Scorpion PMUs

On Fri, Feb 27, 2015 at 07:36:11PM +0000, Stephen Boyd wrote:
> On 02/25/15 08:58, Ashwin Chaugule wrote:
> > Its a count control register (PMxEVCNTCR). Theres various conditions
> > on which you can select when to start/stop counting. e.g. start when
> > another counter register overflows. Setting it to 0 was the
> > recommended default value on Scorpions and Kraits. Reset value is
> > unpredictable. So, just need to make sure this is set every time a
> > counter is setup. Will that still work if this is moved to the reset
> > path?
> 
> I don't think anything in this register changes unless we reset the CPU
> or software changes it, right? We already have a hotplug notifier to
> handle the case where the CPU is hotplugged out (and may get reset) and
> we need to reset the PMU. The other case is deep idle, which we don't
> have yet but we'll need to do a save/reset/restore across idle when we
> get there. So it seems possible to move it to the PMU reset path.

That would be my preference! Please respin the patches and I'll take another
look.

Will
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