linux-kernel - Re: [PATCH v1 3/3] i2c: tegra: Fix suspending in active runtime PM state

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Date:   Fri, 27 Dec 2019 16:55:30 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Wolfram Sang <wsa@...-dreams.de>
Cc:     linux-i2c@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, Mikko Perttunen <cyndis@...si.fi>
Subject: Re: [PATCH v1 3/3] i2c: tegra: Fix suspending in active runtime PM
 state

13.12.2019 17:55, Dmitry Osipenko пишет:
> 13.12.2019 17:29, Dmitry Osipenko пишет:
>> 13.12.2019 02:34, Dmitry Osipenko пишет:
>>> I noticed that sometime I2C clock is kept enabled during suspend-resume.
>>> This happens because runtime PM defers dynamic suspension and thus it may
>>> happen that runtime PM is in active state when system enters into suspend.
>>> In particular I2C controller that is used for CPU's DVFS is often kept ON
>>> during suspend because CPU's voltage scaling happens quite often.
>>>
>>> Note: we marked runtime PM as IRQ-safe during the driver's probe in the
>>> "Support atomic transfers" patch, thus it's okay to enforce runtime PM
>>> suspend/resume in the NOIRQ phase which is used for the system-level
>>> suspend/resume of the driver.
>>>
>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>> ---
>>>  drivers/i2c/busses/i2c-tegra.c | 9 +++++++++
>>>  1 file changed, 9 insertions(+)
>>>
>>> diff --git a/drivers/i2c/busses/i2c-tegra.c b/drivers/i2c/busses/i2c-tegra.c
>>> index b3ecdd87e91f..d309a314f4d6 100644
>>> --- a/drivers/i2c/busses/i2c-tegra.c
>>> +++ b/drivers/i2c/busses/i2c-tegra.c
>>> @@ -1790,9 +1790,14 @@ static int tegra_i2c_remove(struct platform_device *pdev)
>>>  static int __maybe_unused tegra_i2c_suspend(struct device *dev)
>>>  {
>>>  	struct tegra_i2c_dev *i2c_dev = dev_get_drvdata(dev);
>>> +	int err;
>>>  
>>>  	i2c_mark_adapter_suspended(&i2c_dev->adapter);
>>
>> I'm now in a doubt that it is correct to use NOIRQ level at all for the
>> suspend because i2c_mark_adapter_suspended() uses mutex, thus I'm
>> wondering what will happen if there is an asynchronous transfer
>> happening during suspend..
>>
>> The i2c_mark_adapter_suspended() will try to block and will never return?
> 
> Moreover, the I2C interrupt should be disabled during the NOIRQ phase.
> So, yes.. looks like making use of NOIRQ level wasn't a correct
> decision. On the other hand, I don't think that any I2C client driver
> used by Tegra SoCs in the upstream kernel could cause the problem at the
> moment, so it shouldn't be critical.
> 
> BTW: Jon, please CC me next time ;) [I'll try to find a better solution
> for the PCIE problem]

On a second thought, the NOIRQ shouldn't really cause any big problems
because if something executes I2C asynchronously, then the transfer
should simply timeout.