[PATCH v2] perf/arm-cmn: Fix DTC reset

[Geoff Blake]

I've been running this all day on Graviton2 and Graviton3 instances with 
my reproduction method and have not seen it reappear.  From the evidence, 
this has solved the issue.

-Geoff

On Wed, 24 May 2023, Robin Murphy wrote:

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> 
> 
> 
> It turns out that my naive DTC reset logic fails to work as intended,
> since, after checking with the hardware designers, the PMU actually
> needs to be fully enabled in order to correctly clear any pending
> overflows. Therefore, invert the sequence to start with turning on both
> enables so that we can reliably get the DTCs into a known state, then
> moving to our normal counters-stopped state from there. Since all the
> DTM counters have already been unpaired during the initial discovery
> pass, we just need to additionally reset the cycle counters to ensure
> that no other unexpected overflows occur during this period.
> 
> Fixes: 0ba64770a2f2 ("perf: Add Arm CMN-600 PMU driver")
> Reported-by: Geoff Blake <blakgeof at amazon.com>
> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
> ---
> 
> v2: Changed just about everything
> 
>  drivers/perf/arm-cmn.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index b57a0472ea0d..cd2648980540 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -1899,9 +1899,10 @@ static int arm_cmn_init_dtc(struct arm_cmn *cmn, struct arm_cmn_node *dn, int id
>         if (dtc->irq < 0)
>                 return dtc->irq;
> 
> -       writel_relaxed(0, dtc->base + CMN_DT_PMCR);
> +       writel_relaxed(CMN_DT_DTC_CTL_DT_EN, dtc->base + CMN_DT_DTC_CTL);
> +       writel_relaxed(CMN_DT_PMCR_PMU_EN | CMN_DT_PMCR_OVFL_INTR_EN, dtc->base + CMN_DT_PMCR);
> +       writeq_relaxed(0, dtc->base + CMN_DT_PMCCNTR);
>         writel_relaxed(0x1ff, dtc->base + CMN_DT_PMOVSR_CLR);
> -       writel_relaxed(CMN_DT_PMCR_OVFL_INTR_EN, dtc->base + CMN_DT_PMCR);
> 
>         return 0;
>  }
> @@ -1961,7 +1962,7 @@ static int arm_cmn_init_dtcs(struct arm_cmn *cmn)
>                         dn->type = CMN_TYPE_CCLA;
>         }
> 
> -       writel_relaxed(CMN_DT_DTC_CTL_DT_EN, cmn->dtc[0].base + CMN_DT_DTC_CTL);
> +       arm_cmn_set_state(cmn, CMN_STATE_DISABLED);
> 
>         return 0;
>  }
> --
> 2.39.2.101.g768bb238c484.dirty
> 
>