RE: [PATCH v5 2/4] perf: add arm64 smmuv3 pmu driver

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Robin Murphy [mailto:robin.murphy@xxxxxxx]
> Sent: 24 January 2019 18:25
> To: Andrew Murray <andrew.murray@xxxxxxx>; Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@xxxxxxxxxx>
> Cc: lorenzo.pieralisi@xxxxxxx; mark.rutland@xxxxxxx;
> vkilari@xxxxxxxxxxxxxx; neil.m.leeder@xxxxxxxxx;
> jean-philippe.brucker@xxxxxxx; pabba@xxxxxxxxxxxxxx; John Garry
> <john.garry@xxxxxxxxxx>; will.deacon@xxxxxxx; rruigrok@xxxxxxxxxxxxxx;
> Linuxarm <linuxarm@xxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
> linux-acpi@xxxxxxxxxxxxxxx; Guohanjun (Hanjun Guo)
> <guohanjun@xxxxxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v5 2/4] perf: add arm64 smmuv3 pmu driver
> 
> On 23/01/2019 12:14, Andrew Murray wrote:
> [...]
> >>>> +static inline void smmu_pmu_counter_set_value(struct smmu_pmu
> >>> *smmu_pmu,
> >>>> +					      u32 idx, u64 value)
> >>>> +{
> >>>> +	if (smmu_pmu->counter_mask & BIT(32))
> >>>> +		writeq(value, smmu_pmu->reloc_base +
> SMMU_PMCG_EVCNTR(idx,
> >>> 8));
> >>>> +	else
> >>>> +		writel(value, smmu_pmu->reloc_base +
> SMMU_PMCG_EVCNTR(idx,
> >>> 4));
> >>>
> >>> The arm64 IO macros use __force u32 and so it's probably OK to provide a
> 64
> >>> bit
> >>> value to writel. But you could use something like lower_32_bits for clarity.
> >>
> >> Yes, macro uses __force u32. I will change it to make it more clear though.
> 
> To be pedantic, the first cast which the value actually undergoes is to
> (__u32) ;)
> 
> Ultimately, __raw_writel() takes a u32, so in that sense it's never a
> problem to pass a u64, since unsigned truncation is well-defined in the
> C standard. The casting involved in the I/O accessors is mostly about
> going to an endian-specific type and back again.
> 
> [...]
> >>>> +static void smmu_pmu_event_start(struct perf_event *event, int flags)
> >>>> +{
> >>>> +	struct smmu_pmu *smmu_pmu = to_smmu_pmu(event->pmu);
> >>>> +	struct hw_perf_event *hwc = &event->hw;
> >>>> +	int idx = hwc->idx;
> >>>> +	u32 filter_span, filter_sid;
> >>>> +	u32 evtyper;
> >>>> +
> >>>> +	hwc->state = 0;
> >>>> +
> >>>> +	smmu_pmu_set_period(smmu_pmu, hwc);
> >>>> +
> >>>> +	smmu_pmu_get_event_filter(event, &filter_span, &filter_sid);
> >>>> +
> >>>> +	evtyper = get_event(event) |
> >>>> +		  filter_span << SMMU_PMCG_SID_SPAN_SHIFT;
> >>>> +
> >>>> +	smmu_pmu_set_evtyper(smmu_pmu, idx, evtyper);
> >>>> +	smmu_pmu_set_smr(smmu_pmu, idx, filter_sid);
> >>>> +	smmu_pmu_interrupt_enable(smmu_pmu, idx);
> >>>> +	smmu_pmu_counter_enable(smmu_pmu, idx);
> >>>> +}
> >>>> +
> >>>> +static void smmu_pmu_event_stop(struct perf_event *event, int flags)
> >>>> +{
> >>>> +	struct smmu_pmu *smmu_pmu = to_smmu_pmu(event->pmu);
> >>>> +	struct hw_perf_event *hwc = &event->hw;
> >>>> +	int idx = hwc->idx;
> >>>> +
> >>>> +	if (hwc->state & PERF_HES_STOPPED)
> >>>> +		return;
> >>>> +
> >>>> +	smmu_pmu_counter_disable(smmu_pmu, idx);
> >>>
> >>> Is it intentional not to call smmu_pmu_interrupt_disable here?
> >>
> >> Yes, it is. Earlier patch had the interrupt toggling and Robin pointed out that
> >> it is not really needed as counters are anyway stopped and explicitly
> disabling
> >> may not solve the spurious interrupt case as well.
> >>
> >
> > Ah apologies for not seeing that in earlier reviews.
> 
> Hmm, I didn't exactly mean "keep enabling it every time an event is
> restarted and never disable it anywhere", though. I was thinking more
> along the lines of enabling in event_add() and disabling in event_del()
> (i.e. effectively tying it to allocation and deallocation of the counter).
> 

Right. I missed the point that it was not disabled at all!. I will rearrange it 
to _add/_del path. 

Thanks for all the comments. I am planning to send out a v6 soon. 
Between, did you get a chance to take a look at patch #4 (HiSilicon erratum one) ? 
Appreciate if you could take a look and let me know before v6.

Thanks,
Shameer