linux-kernel - Re: [PATCH] mfd: tps6586x: Handle interrupts on suspend

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Date:   Wed, 24 Oct 2018 15:19:12 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>
CC:     Lee Jones <lee.jones@...aro.org>, <linux-kernel@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH] mfd: tps6586x: Handle interrupts on suspend


On 24/10/2018 13:44, Dmitry Osipenko wrote:
> On 10/24/18 1:49 PM, Jon Hunter wrote:
>>
>> On 22/10/2018 12:19, Dmitry Osipenko wrote:
>>> On 10/22/18 12:52 PM, Thierry Reding wrote:
>>>> On Fri, Oct 19, 2018 at 02:22:53PM +0100, Jon Hunter wrote:
>>>>> From: Jonathan Hunter <jonathanh@...dia.com>
>>>>>
>>>>> The tps6586x driver creates an irqchip that is used by its various child
>>>>> devices for managing interrupts. The tps6586x-rtc device is one of its
>>>>> children that uses the tps6586x irqchip. When using the tps6586x-rtc as
>>>>> a wake-up device from suspend, the following is seen:
>>>>>
>>>>>  PM: Syncing filesystems ... done.
>>>>>  Freezing user space processes ... (elapsed 0.001 seconds) done.
>>>>>  OOM killer disabled.
>>>>>  Freezing remaining freezable tasks ... (elapsed 0.000 seconds) done.
>>>>>  Disabling non-boot CPUs ...
>>>>>  Entering suspend state LP1
>>>>>  Enabling non-boot CPUs ...
>>>>>  CPU1 is up
>>>>>  tps6586x 3-0034: failed to read interrupt status
>>>>>  tps6586x 3-0034: failed to read interrupt status
>>>>>
>>>>> The reason why the tps6586x interrupt status cannot be read is because
>>>>> the tps6586x interrupt is not masked during suspend and when the
>>>>> tps6586x-rtc interrupt occurs, to wake-up the device, the interrupt is
>>>>> seen before the i2c controller has been resumed in order to read the
>>>>> tps6586x interrupt status.
>>>>>
>>>>> The tps6586x-rtc driver sets it's interrupt as a wake-up source during
>>>>> suspend, which gets propagated to the parent tps6586x interrupt.
>>>>> However, the tps6586x-rtc driver cannot disable it's interrupt during
>>>>> suspend otherwise we would never be woken up and so the tps6586x must
>>>>> disable it's interrupt instead.
>>>>>
>>>>> Prevent the tps6586x interrupt handler from executing on exiting suspend
>>>>> before the i2c controller has been resumed by disabling the tps6586x
>>>>> interrupt on entering suspend and re-enabling it on resuming from
>>>>> suspend.
>>>>>
>>>>> Cc: stable@...r.kernel.org
>>>>>
>>>>> Signed-off-by: Jon Hunter <jonathanh@...dia.com>
>>>>> ---
>>>>>  drivers/mfd/tps6586x.c | 24 ++++++++++++++++++++++++
>>>>>  1 file changed, 24 insertions(+)
>>>>
>>>> So does this mean that the SPI interrupt for the PMIC can still be a
>>>> wakeup source even if it is masked? This is slightly odd because now
>>>> you're saying that this does work while it doesn't work for the RTC
>>>> interrupt. So is this an implementation quirk of the LIC/GIC on Tegra
>>>> which doesn't extend to the TPS6586x? Or am I missing something?
>>>
>>> What is the expected behaviour of IRQ disabling? Should it disable wakeup ability or only mask IRQ handling?
>>
>> I believe only mask the interrupt. However, the caveat here could be if
>> the parent interrupt controller actually supports wake-up. For Tegra it
>> is the LIC that handles the wake-up.
>>
>>> Couple months ago disabling of IRQ was disabling the wakeup, now something has been changed in kernel and wakeup isn't getting disabled. So either there was a bug before that was fixed or there is a bug now.
>>
>> Are you sure you were disabling the PMIC host interrupt? If you disable
>> the RTC interrupt in the PMIC's RTC driver, then this will prevent the
>> wake-up from occurring because you are masking the interrupt within the
>> PMIC and so it will never generate an interrupt to the host.
> 
> I'm pretty sure (but not 100%) that was trying the same change as in your patch and it didn't work sometime before. If disable_irq() shouldn't disable wakeup, then everything is perfect now.

Please note that this is very similar to the following fix where I
experienced the same problem with another PMIC a couple years back ...

35deff7eb212 ("mfd: as3722: Handle interrupts on suspend")

I did not bother setting the enable/disable_irq_wake() for the tps6586x
host irq during resume/suspend because the irqchip for the tps6586x has
an irq_set_wake function that propagates the wake enable/disable.

Cheers
Jon

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