linux-kernel - Re: [PATCH v4 07/16] PM / devfreq: tegra: Properly disable interrupts

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Date:   Fri, 7 Jun 2019 19:58:20 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 07/16] PM / devfreq: tegra: Properly disable interrupts

05.06.2019 1:55, Dmitry Osipenko пишет:
> 04.06.2019 16:40, Dmitry Osipenko пишет:
>> 04.06.2019 14:07, Thierry Reding пишет:
>>> On Thu, May 02, 2019 at 02:38:06AM +0300, Dmitry Osipenko wrote:
>>>> There is no guarantee that interrupt handling isn't running in parallel
>>>> with tegra_actmon_disable_interrupts(), hence it is necessary to protect
>>>> DEV_CTRL register accesses and clear IRQ status with ACTMON's IRQ being
>>>> disabled in the Interrupt Controller in order to ensure that device
>>>> interrupt is indeed being disabled.
>>>>
>>>> Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
>>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>>> ---
>>>>  drivers/devfreq/tegra-devfreq.c | 21 +++++++++++++++------
>>>>  1 file changed, 15 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/devfreq/tegra-devfreq.c b/drivers/devfreq/tegra-devfreq.c
>>>> index b65313fe3c2e..ce1eb97a2090 100644
>>>> --- a/drivers/devfreq/tegra-devfreq.c
>>>> +++ b/drivers/devfreq/tegra-devfreq.c
>>>> @@ -171,6 +171,8 @@ struct tegra_devfreq {
>>>>  	struct notifier_block	rate_change_nb;
>>>>  
>>>>  	struct tegra_devfreq_device devices[ARRAY_SIZE(actmon_device_configs)];
>>>> +
>>>> +	int irq;
>>>
>>> Interrupts are typically unsigned int.
>>>
>>>>  };
>>>>  
>>>>  struct tegra_actmon_emc_ratio {
>>>> @@ -417,6 +419,8 @@ static void tegra_actmon_disable_interrupts(struct tegra_devfreq *tegra)
>>>>  	u32 val;
>>>>  	unsigned int i;
>>>>  
>>>> +	disable_irq(tegra->irq);
>>>> +
>>>>  	for (i = 0; i < ARRAY_SIZE(tegra->devices); i++) {
>>>>  		dev = &tegra->devices[i];
>>>>  
>>>> @@ -427,9 +431,14 @@ static void tegra_actmon_disable_interrupts(struct tegra_devfreq *tegra)
>>>>  		val &= ~ACTMON_DEV_CTRL_CONSECUTIVE_ABOVE_WMARK_EN;
>>>>  
>>>>  		device_writel(dev, val, ACTMON_DEV_CTRL);
>>>> +
>>>> +		device_writel(dev, ACTMON_INTR_STATUS_CLEAR,
>>>> +			      ACTMON_DEV_INTR_STATUS);
>>>>  	}
>>>>  
>>>>  	actmon_write_barrier(tegra);
>>>> +
>>>> +	enable_irq(tegra->irq);
>>>
>>> Why do we enable interrupts after this? Is there any use in having the
>>> top-level interrupt enabled if nothing's going to generate an interrupt
>>> anyway?
>>
>> There is no real point in having the interrupt enabled other than to
>> keep the enable count balanced.
>>
>> IIUC, we will need to disable IRQ at the driver's probe time (after
>> requesting the IRQ) if we want to avoid that (not really necessary)
>> balancing. This is probably something that could be improved in a
>> follow-up patches, if desired.
> 
> Nah, it's not worth the effort. It is quite problematic that we can't
> keep interrupt disabled during of devfreq_add_device() execution because
> it asks governor to enable the interrupt and the interrupt shall be
> disabled because we're using device's lock in the governor interrupt
> handler.. device is getting assigned only after completion of the
> devfreq_add_device() and hence ISR gets a NULL deref if it is fired
> before device is assigned. So I'll leave this part as-is.
> 
> Thierry, please answer to all of the remaining patches where you had
> some concerns. I'll send out another series on top of this, addressing
> yours comments and fixing another bug that I spotted today.
> 

I looked at this once again and found that the interrupt could be kept
disabled on request using the IRQ_NOAUTOEN flag and then the device
could be assigned within the governor's event handler, so everything is
resolved very nicely! :)

I'll send patches addressing this comment and the rest after getting
relies from you guys. Please try to not postpone the responses too much
as more interactivity in a review/apply process usually help quite a
lot, thanks in advance!