linux-kernel - Re: [PATCH 3/7] ARM: perf_event: Add basic support for Krait CPU PMUs

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Message-ID: <20140110110114.GC10455@mudshark.cambridge.arm.com>
Date:	Fri, 10 Jan 2014 11:01:14 +0000
From:	Will Deacon <will.deacon@....com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	"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>,
	Neil Leeder <nleeder@...eaurora.org>,
	Ashwin Chaugule <ashwinc@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	mark.rutland@....com
Subject: Re: [PATCH 3/7] ARM: perf_event: Add basic support for Krait CPU PMUs

On Thu, Jan 09, 2014 at 07:57:12PM +0000, Stephen Boyd wrote:
> (Adding DT reviewers)
> 
> On 01/09/14 03:04, Will Deacon wrote:
> > On Wed, Jan 08, 2014 at 10:59:40PM +0000, Stephen Boyd wrote:
> >
> >> +static int krait_pmu_init(struct arm_pmu *cpu_pmu)
> >> +{
> >> +	u32 id = read_cpuid_id() & 0xffffff00;
> >> +
> >> +	armv7pmu_init(cpu_pmu);
> >> +	cpu_pmu->name		= "ARMv7 Krait";
> >> +	/* Some early versions of Krait don't support PC write events */
> >> +	if (id == 0x511f0400 || id == 0x510f0600)
> >> +		cpu_pmu->map_event	= krait_map_event_no_branch;
> > Hmm, I'd really rather this information came via the DT. In fact, you could
> > just drop the branch event from your main map_event_function and keep things
> > simple. It depends how badly you want to advertise it in perf list :)
> >
> 
> Not every version of Krait is missing support for this event, so I'd
> like to keep it so things like perf stat show branch counts. How about I
> add a bool property to the pmu node indicating that this PMU is missing
> support for the PC write events? Something like "no-pc-write"?

Perhaps, although I think it should be qualcomm-specific, so something like
"qcom,krait-no-pc-write"? Again, I'd be glad to hear something from a DT
reviewer on this.

Will
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