linux-kernel - Re: [PATCH v2 1/2] i2c: tegra: Better handle case where CPU0 is busy for a long time

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Date:   Wed, 29 Apr 2020 02:12:18 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Jon Hunter <jonathanh@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Manikanta Maddireddy <mmaddireddy@...dia.com>,
        Vidya Sagar <vidyas@...dia.com>
Cc:     linux-i2c@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 1/2] i2c: tegra: Better handle case where CPU0 is busy
 for a long time

28.04.2020 11:02, Jon Hunter пишет:
> 
> On 27/04/2020 16:38, Dmitry Osipenko wrote:
>> 27.04.2020 17:45, Dmitry Osipenko пишет:
>>> 27.04.2020 17:13, Dmitry Osipenko пишет:
>>>> 27.04.2020 15:46, Dmitry Osipenko пишет:
>>>>> 23.04.2020 13:56, Jon Hunter пишет:
>>>>>>>> So I think that part of the problem already existed prior to these
>>>>>>>> patches. Without your patches I see ...
>>>>>>>>
>>>>>>>> [   59.543528] tegra-i2c 7000d000.i2c: i2c transfer timed out
>>>>>>>> [   59.549036] vdd_sata,avdd_plle: failed to disable
>>>>>>>> [   59.553778] Failed to disable avdd-plle: -110
>>>>>>>> [   59.558150] tegra-pcie 3000.pcie: failed to disable regulators: -110
>>>>>>> Does this I2C timeout happen with my patches? Could you please post full
>>>>>>> logs of an older and the recent kernel versions?
>>>>>> I believe that it does, but I need to check.
>>>>>>
>>>>>
>>>>> Jon, could you please confirm that you're seeing those regulator-disable
>>>>> errors with my patch? I don't see those errors in yours original log [1].
>>>>>
>>>>> [1]
>>>>> https://lore.kernel.org/lkml/1e259e22-c300-663a-e537-18d854e0f478@nvidia.com/
>>>>>
>>>>> Again, could you please post the *full* logs?
>>>>>
>>>>> If regulator's disabling was "failing" before without my patch because
>>>>> of the I2C interrupt being force-disabled during of NOIRQ phase, and now
>>>>> regulator's disabling succeeds with my patch because IRQ is manually
>>>>> handled after the timeout, then this could be bad. It means that
>>>>> regulator was actually getting disabled, but I2C driver was timing out
>>>>> because interrupt couldn't be handled in NOIRQ phase, which should
>>>>> result in a dead PCIe on a resume from suspend since regulator's core
>>>>> thinks that regulator is enabled (I2C said it failed to disable), while
>>>>> it is actually disabled.
>>>>>
>>>>> Do you have anything plugged into the PCIe slot in yours testing farm?
>>>>> It wouldn't surprise me if the plugged card isn't functional after
>>>>> resume from suspend on a stable kernels.
>>>>>
>>>>
>>>> I actually now see that interrupt is not allowed to be enabled during
>>>> the NOIRQ phase:
>>>>
>>>> https://elixir.bootlin.com/linux/v5.7-rc3/source/kernel/irq/manage.c#L640
>>>>
>>>> it should be worthwhile to turn it into a WARN_ON.
>>>>
>>>
>>> Oh, wait! There is already a warning there.. hmm.
>>>
>>
>> Aha, the disable depth for the I2C interrupt is 2 after
>> suspend_device_irq(), that's why there is no warning.
>>
>> This should catch the bug and trigger the warning:
>>
>> --- >8 ---
>> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
>> index 453a8a0f4804..fe25104d8b22 100644
>> --- a/kernel/irq/manage.c
>> +++ b/kernel/irq/manage.c
>> @@ -653,6 +653,8 @@ void __enable_irq(struct irq_desc *desc)
>>  		break;
>>  	}
>>  	default:
>> +		if (desc->istate & IRQS_SUSPENDED)
>> +			goto err_out;
>>  		desc->depth--;
>>  	}
>>  }
>> --- >8 ---
>>
>> Jon could you please give it a try? Will this change produce a warning
>> for the I2C driver on a PCIe suspend for the v5.6 kernel?
> 
> 
> Yes I can test, but I still want to know why resume is currently broken.

BTW, I guess we could use the IRQF_NO_SUSPEND flag for I2C interrupt.
Then it should be possible to use I2C in the late suspend without the
need for atomic transfers, once RPM is resolved.