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

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Message-ID: <f78bb10c-0744-4a23-c584-0212dd9fb491@nvidia.com>
Date:   Tue, 28 Apr 2020 09:02:36 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.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


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.

Jon

-- 
nvpublic