netdev - Re: [PATCH] net: wwan: qcom_bam_dmux: Fix missing pm_runtime

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Message-ID: <04cf9e68-ef69-dade-0b56-205a3aa4e653@huawei.com>
Date: Mon, 23 Sep 2024 10:25:28 +0800
From: Jinjie Ruan <ruanjinjie@...wei.com>
To: Stephan Gerhold <stephan.gerhold@...aro.org>, Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>
CC: <stephan@...hold.net>, <loic.poulain@...aro.org>,
	<ryazanov.s.a@...il.com>, <johannes@...solutions.net>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<netdev@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH] net: wwan: qcom_bam_dmux: Fix missing
 pm_runtime_disable()



On 2024/9/20 21:38, Stephan Gerhold wrote:
> On Fri, Sep 20, 2024 at 03:05:13PM +0200, Dmitry Baryshkov wrote:
>> On Fri, 20 Sept 2024 at 14:44, Stephan Gerhold
>> <stephan.gerhold@...aro.org> wrote:
>>>
>>> On Fri, Sep 20, 2024 at 01:48:15PM +0300, Dmitry Baryshkov wrote:
>>>> On Fri, Sep 20, 2024 at 06:07:11PM GMT, Jinjie Ruan wrote:
>>>>> It's important to undo pm_runtime_use_autosuspend() with
>>>>> pm_runtime_dont_use_autosuspend() at driver exit time.
>>>>>
>>>>> But the pm_runtime_disable() and pm_runtime_dont_use_autosuspend()
>>>>> is missing in the error path for bam_dmux_probe(). So add it.
>>>>
>>>> Please use devm_pm_runtime_enable(), which handles autosuspend.
>>>>
>>>
>>> This would conflict with the existing cleanup in bam_dmux_remove(),
>>> which probably needs to stay manually managed since the tear down order
>>> is quite important there.
>>
>> Hmm, the setup and teardown code makes me wonder now.
> 
> Yeah, you ask the right questions. :-) It's really tricky to get this
> 100% right. I spent quite some time to get close, but there are likely
> still some loopholes. I haven't heard of anyone running into trouble,
> though. This driver has been rock solid for the past few years.
> 
>> Are we guaranteed that the IRQs can not be delivered after suspending
>> the device?
> 
> I think bam_dmux_remove() should be safe. disable_irq(dmux->pc_irq)
> prevents any further delivery of IRQs before doing the final power off.
> 
>> Also is there a race between IRQs being enabled, manual check of the
>> IRQ state and the pc_ack / power_off calls?
> 
> Yes, I'm pretty sure this race exists in theory. I'm not sure how to
> avoid it. We would need an atomic "return current state and enable IRQ"
> operation, but I don't think this exists at the moment. Do you have any
> suggestions?

Maybe use IRQF_NO_AUTOEN flag to reuqest irq and enable_irq() after that?

> 
> Thanks,
> Stephan