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

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Message-ID: <1607565387.25719.43.camel@mhfsdcap03>
Date:   Thu, 10 Dec 2020 09:56:27 +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 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);
        	resume_device_irqs();
        	device_wakeup_disarm_wake_irqs();
        	cpuidle_resume();
	}
.master_xfer_atomic() seems to be invalid for this question at this
time?