On 20 February 2015 at 15:16, Stephen Boyd <sboyd@xxxxxxxxxxxxxx> 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, ®ion, &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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