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

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Message-ID: <042bbb32-481e-40d8-a46a-472b724ec33f@arm.com>
Date: Fri, 5 Apr 2024 11:33:51 +0100
From: Robin Murphy <robin.murphy@....com>
To: Ilkka Koskinen <ilkka@...amperecomputing.com>,
 Besar Wicaksono <bwicaksono@...dia.com>,
 Suzuki K Poulose <suzuki.poulose@....com>, Will Deacon <will@...nel.org>
Cc: 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 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?

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)