linux-kernel - Re: [PATCH] perf: arm_cspmu: Don't touch interrupt registers if no interrupt was assigned

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Date: Fri, 5 Apr 2024 15:33:47 -0700 (PDT)
From: Ilkka Koskinen <ilkka@...amperecomputing.com>
To: Robin Murphy <robin.murphy@....com>
cc: Ilkka Koskinen <ilkka@...amperecomputing.com>, 
    Besar Wicaksono <bwicaksono@...dia.com>, 
    Suzuki K Poulose <suzuki.poulose@....com>, Will Deacon <will@...nel.org>, 
    Mark Rutland <mark.rutland@....com>, Raag Jadav <raag.jadav@...el.com>, 
    linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [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@...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)
>