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: <75ed1065-d123-9193-7017-cce12889130b@quicinc.com>
Date: Mon, 24 Jun 2024 14:26:52 +0530
From: Sibi Sankar <quic_sibis@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>
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 6/21/24 11:15, Bjorn Andersson 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
> 
> 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.

Ack, will make the changes in the next re-spin.

-Sibi

> 
> 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
>>