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

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Message-ID: <e83ab23b-81f2-620c-039b-9cadd84a39fa@ti.com>
Date:   Thu, 10 Dec 2020 15:03:52 +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 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?

Is "some device" in Kernel mainline?

>          	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