linux-kernel - Re: [PATCH V2 2/3] soc: qcom: icc-bwmon: Allow for interrupts to be shared across instances

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Message-ID: <vjes4lm3um44f6oguvrq3gozemquzmmmicj47ieczwfuqkmaqp@aby3dj6ttdig>
Date: Fri, 21 Jun 2024 00:45:14 -0500
From: Bjorn Andersson <andersson@...nel.org>
To: Sibi Sankar <quic_sibis@...cinc.com>
Cc: konrad.dybcio@...aro.org, djakov@...nel.org, robh+dt@...nel.org, 
	krzysztof.kozlowski+dt@...aro.org, srinivas.kandagatla@...aro.org, linux-kernel@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org, linux-pm@...r.kernel.org, 
	quic_rgottimu@...cinc.com, quic_kshivnan@...cinc.com, conor+dt@...nel.org, 
	dmitry.baryshkov@...aro.org, abel.vesa@...aro.org
Subject: Re: [PATCH V2 2/3] soc: qcom: icc-bwmon: Allow for interrupts to be
 shared across instances

On Tue, Jun 18, 2024 at 09:13:05PM GMT, Sibi Sankar wrote:
> The multiple BWMONv4 instances available on the X1E80100 SoC use the
> same interrupt number. Mark them are shared to allow for re-use across
> instances. Handle the ensuing race introduced by relying on bwmon_disable

In an effort to educate the reader, could you please describe what the
race condition is here.

It would also make sense to break this ("Handle...") into a separate
paragraph.

Regards,
Bjorn

> to disable the interrupt and coupled with explicit request/free irqs.
> 
> Signed-off-by: Sibi Sankar <quic_sibis@...cinc.com>
> ---
> 
> v2:
> * Use explicit request/free irq and add comments regarding the race
>   introduced when adding the IRQF_SHARED flag. [Krzysztof/Dmitry]
> 
>  drivers/soc/qcom/icc-bwmon.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/soc/qcom/icc-bwmon.c b/drivers/soc/qcom/icc-bwmon.c
> index fb323b3364db..4a4e28b41509 100644
> --- a/drivers/soc/qcom/icc-bwmon.c
> +++ b/drivers/soc/qcom/icc-bwmon.c
> @@ -781,9 +781,10 @@ static int bwmon_probe(struct platform_device *pdev)
>  	bwmon->dev = dev;
>  
>  	bwmon_disable(bwmon);
> -	ret = devm_request_threaded_irq(dev, bwmon->irq, bwmon_intr,
> -					bwmon_intr_thread,
> -					IRQF_ONESHOT, dev_name(dev), bwmon);
> +
> +	/* SoCs with multiple cpu-bwmon instances can end up using a shared interrupt line */
> +	ret = request_threaded_irq(bwmon->irq, bwmon_intr, bwmon_intr_thread,
> +				   IRQF_ONESHOT | IRQF_SHARED, dev_name(dev), bwmon);
>  	if (ret)
>  		return dev_err_probe(dev, ret, "failed to request IRQ\n");
>  
> @@ -798,6 +799,13 @@ static void bwmon_remove(struct platform_device *pdev)
>  	struct icc_bwmon *bwmon = platform_get_drvdata(pdev);
>  
>  	bwmon_disable(bwmon);
> +
> +	/*
> +	 * Handle the race introduced, when dealing with multiple bwmon instances
> +	 * using a shared interrupt line, by relying on bwmon_disable to disable
> +	 * the interrupt and followed by an explicit free.
> +	 */
> +	free_irq(bwmon->irq, bwmon);
>  }
>  
>  static const struct icc_bwmon_data msm8998_bwmon_data = {
> -- 
> 2.34.1
>