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: <2f238fe4-aa67-b311-7c76-a67359587268@quicinc.com>
Date: Mon, 24 Jun 2024 14:28:48 +0530
From: Sibi Sankar <quic_sibis@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: <andersson@...nel.org>, <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>,
        <abel.vesa@...aro.org>
Subject: Re: [PATCH V2 2/3] soc: qcom: icc-bwmon: Allow for interrupts to be
 shared across instances



On 6/19/24 00:25, Dmitry Baryshkov wrote:
> 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
>> 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 */
> 
> ... using devm_ here might result in the IRQ handler being executed
> after bwmon_disable in bwmon_remove()

Ack

> 
>> +	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.
>> +	 */
> 
> This sounds more like a part of the commit message. The comment before
> request_threaded_irq() should be enough.

Ack

-Sibi

> 
>> +	free_irq(bwmon->irq, bwmon);
>>   }
>>   
>>   static const struct icc_bwmon_data msm8998_bwmon_data = {
>> -- 
>> 2.34.1
>>
>