linux-kernel - Re: [v2] i2c: mediatek: Move suspend and resume handling to NOIRQ phase

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Message-ID: <765c182a-5c68-b408-85ca-f757e891090e@ti.com>
Date:   Mon, 14 Dec 2020 22:08:16 +0200
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Qii Wang <qii.wang@...iatek.com>
CC:     Wolfram Sang <wsa@...-dreams.de>, <matthias.bgg@...il.com>,
        <linux-i2c@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>,
        <srv_heupstream@...iatek.com>, <leilk.liu@...iatek.com>
Subject: Re: [v2] i2c: mediatek: Move suspend and resume handling to NOIRQ
 phase



On 14/12/2020 10:48, Qii Wang wrote:
> On Thu, 2020-12-10 at 15:03 +0200, Grygorii Strashko wrote:
>>
>> On 10/12/2020 03:56, Qii Wang wrote:
>>> On Mon, 2020-12-07 at 18:35 +0200, Grygorii Strashko wrote:
>>>>
>>>>>
>>>>> On Thu, 2020-12-03 at 10:01 +0200, Grygorii Strashko wrote:
>>>>>>
>>>>>> On 03/12/2020 03:25, Qii Wang wrote:
>>>>>>> On Wed, 2020-12-02 at 16:35 +0100, Wolfram Sang wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>>> Some i2c device driver indirectly uses I2C driver when it is now
>>>>>>>>> being suspended. The i2c devices driver is suspended during the
>>>>>>>>> NOIRQ phase and this cannot be changed due to other dependencies.
>>>>>>>>> Therefore, we also need to move the suspend handling for the I2C
>>>>>>>>> controller driver to the NOIRQ phase as well.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Qii Wang <qii.wang@...iatek.com>
>>>>>>>>
>>>>>>>> Is this a bugfix and should go into 5.10? Or can it wait for 5.11?
>>>>>>>>
>>>>>>>
>>>>>>> Yes, Can you help to apply it into 5.10? Thanks
>>>>>>
>>>>>> To be honest if you still do have any i2c device which accessing i2c buss after _noirq
>>>>>> stage and your driver does not implement .master_xfer_atomic() - you definitely have a bigger problem.
>>>>>> So adding IRQF_NO_SUSPEND sound like a hack and probably works just by luck.
>>>>>>
>>>>>
>>>>> At present, it is only a problem caused by missing interrupts,
>>>>> and .master_xfer_atomic() just a implement in polling mode. Why not set
>>>>> the interrupt to a state that can always be triggered?
>>>>>
>>>>>
>>>>
>>>> Because you must not use any IRQ driven operations after _noirq suspend state as it might (and most probably will)
>>>> cause unpredictable behavior later  in suspend_enter():
>>>>
>>>> 	arch_suspend_disable_irqs();
>>>> 	BUG_ON(!irqs_disabled());
>>>> ^after this point any IRQ driven I2C transfer will cause IRQ to be re-enabled
>>>>
>>>> if you need  turn off device from platform callbacks -  .master_xfer_atomic() has to be implemented and used.
>>>>     
>>> Maybe my comment is a bit disturbing.Our purpose is not to call i2c and
>>> use interrupts after _noirq pauses.So We use
>>> i2c_mark_adapter_suspended&i2c_mark_adapter_resumed to block these i2c
>>> transfers， There will not have any IRQ driven I2C transfer after this
>>> point:
>>>           arch_suspend_disable_irqs();
>>>           BUG_ON(!irqs_disabled());
>>> But some device driver will do i2c transfer after
>>> dpm_noirq_resume_devices in dpm_resume_noirq(PMSG_RESUME) when our
>>> driver irq hasn't resume.
>>> 	void dpm_resume_noirq(pm_message_t state)
>>> 	{
>>>           	dpm_noirq_resume_devices(state);
>>
>> Just to clarify. You have resume sequence in dpm_noirq_resume_devices
>>    dpm_noirq_resume_devices -> resume I2C -> resume some device -> do i2c transfer after?
>>
> 
> Yes.

huh. First consider IRQF_EARLY_RESUME - it's better, but still will be a hack

> 
>> Is "some device" in Kernel mainline?
>>
> 
> The problematic device driver is drivers/regulator/da9211-regulator.c in
> Kernel mainline.

regulator is passive device, somebody should call it !?

And da9211-regulator IRQ handler should remain disabled till resume_device_irqs() call.

note. regulator_class implements only

static const struct dev_pm_ops __maybe_unused regulator_pm_ops = {
	.suspend	= regulator_suspend,
	.resume		= regulator_resume,
};


> 
>>>           	resume_device_irqs();
>>>           	device_wakeup_disarm_wake_irqs();
>>>           	cpuidle_resume();
>>> 	}
>>> .master_xfer_atomic() seems to be invalid for this question at this
>>> time?
>>>
>>
> 

-- 
Best regards,
grygorii