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

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Message-ID: <1607935685.25719.49.camel@mhfsdcap03>
Date:   Mon, 14 Dec 2020 16:48:05 +0800
From:   Qii Wang <qii.wang@...iatek.com>
To:     Grygorii Strashko <grygorii.strashko@...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 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.

> Is "some device" in Kernel mainline?
> 

The problematic device driver is drivers/regulator/da9211-regulator.c 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?
> > 
>