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SubjectRe: [PATCH] perf: arm_cspmu: Don't touch interrupt registers if no interrupt was assigned

On Fri, 5 Apr 2024, Robin Murphy wrote:
> On 2024-03-07 7:31 pm, Ilkka Koskinen wrote:
>> The driver enabled and disabled interrupts even if no interrupt was
>> assigned to the device.
>
> Why's that a concern - if the interrupt isn't routed anywhere, surely it
> makes no difference what happens at the source end?

The issue is that we have two PMUs attached to the same interrupt line.
Unfortunately, I just don't seem to find time to add support for shared
interrupts to the cspmu driver. Meanwhile, I assigned the interrupt
to one of the PMUs while the other one has zero in the APMT table. Without
the patch, I can trigger "ghost interrupt" in the latter PMU.

Cheers, Ilkka

>
> Thanks,
> Robin.
>
>> Signed-off-by: Ilkka Koskinen <ilkka@os.amperecomputing.com>
>> ---
>> drivers/perf/arm_cspmu/arm_cspmu.c | 6 ++++--
>> 1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/perf/arm_cspmu/arm_cspmu.c
>> b/drivers/perf/arm_cspmu/arm_cspmu.c
>> index 50b89b989ce7..2cbdb5dcb6ff 100644
>> --- a/drivers/perf/arm_cspmu/arm_cspmu.c
>> +++ b/drivers/perf/arm_cspmu/arm_cspmu.c
>> @@ -795,7 +795,8 @@ static void arm_cspmu_enable_counter(struct arm_cspmu
>> *cspmu, int idx)
>> inten_off = PMINTENSET + (4 * reg_id);
>> cnten_off = PMCNTENSET + (4 * reg_id);
>> - writel(BIT(reg_bit), cspmu->base0 + inten_off);
>> + if (cspmu->irq)
>> + writel(BIT(reg_bit), cspmu->base0 + inten_off);
>> writel(BIT(reg_bit), cspmu->base0 + cnten_off);
>> }
>> @@ -810,7 +811,8 @@ static void arm_cspmu_disable_counter(struct
>> arm_cspmu *cspmu, int idx)
>> cnten_off = PMCNTENCLR + (4 * reg_id);
>> writel(BIT(reg_bit), cspmu->base0 + cnten_off);
>> - writel(BIT(reg_bit), cspmu->base0 + inten_off);
>> + if (cspmu->irq)
>> + writel(BIT(reg_bit), cspmu->base0 + inten_off);
>> }
>> static void arm_cspmu_event_update(struct perf_event *event)
>

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