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

[Grygorii Strashko]

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@xxxxxxxxxxxx>
> > > > > >
> > > > > > 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