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

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Date:	Tue, 24 Feb 2015 12:23:36 -0500
From:	Ashwin Chaugule <ashwin.chaugule@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Will Deacon <will.deacon@....com>,
	"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 20 February 2015 at 15:16, Stephen Boyd <sboyd@...eaurora.org> wrote:
> On 02/20, Will Deacon wrote:
>> On Fri, Feb 13, 2015 at 06:24:09PM +0000, Stephen Boyd wrote:
>>
>> > +static void scorpion_evt_setup(int idx, u32 config_base)
>> > +{
>> > +       u32 val;
>> > +       u32 mask;
>> > +       u32 vval, fval;
>> > +       unsigned int region;
>> > +       unsigned int group;
>> > +       unsigned int code;
>> > +       unsigned int group_shift;
>> > +       bool venum_event;
>> > +
>> > +       krait_decode_event(config_base, &region, &group, &code, &venum_event,
>> > +                          NULL);
>> > +
>> > +       group_shift = group * 8;
>> > +       mask = 0xff << group_shift;
>> > +
>> > +       /* Configure evtsel for the region and group */
>> > +       if (venum_event)
>> > +               val = SCORPION_VLPM_GROUP0;
>> > +       else
>> > +               val = scorpion_get_pmresrn_event(region);
>> > +       val += group;
>> > +       /* Mix in mode-exclusion bits */
>> > +       val |= config_base & (ARMV7_EXCLUDE_USER | ARMV7_EXCLUDE_PL1);
>> > +       armv7_pmnc_write_evtsel(idx, val);
>> > +
>> > +       asm volatile("mcr p15, 0, %0, c9, c15, 0" : : "r" (0));
>>
>> What's this guy doing?
>
> This is the same as Krait. It's clearing some implementation
> defined register. From what I can tell it's a per-event register
> (i.e. PMSELR decides which event this register write actually
> affects) and we do this here to reset this register to some
> defined value, zero. Otherwise the reset value of this register
> is UNPREDICTABLE and that would be bad. I think we might be able
> to move it to the pmu reset path, but I don't know. Ashwin?

Will have to check once I get to office tomorrow.
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