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RE: [PATCH v1] Input: tegra-kbc - report wakeup key for some platforms.

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From: Dmitry Torokhov [dmitry.torokhov@xxxxxxxxx]
Sent: Sunday, December 04, 2011 8:27 PM
To: Rakesh Iyer
Cc: rydberg@xxxxxxxxxxx; Stephen Warren; Laxman Dewangan; linux-kernel@xxxxxxxxxxxxxxx; linux-input@xxxxxxxxxxxxxxx; linux-tegra@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v1] Input: tegra-kbc - report wakeup key for some platforms.

On Sun, Dec 04, 2011 at 05:18:17PM -0800, riyer wrote:
> Hello Dmitry.
> Please find replies inline.
> On Sun, 2011-12-04 at 00:50 -0800, Dmitry Torokhov wrote:
> > Hi Rakesh,
> >
> > On Thu, Dec 01, 2011 at 01:09:59PM -0800, Rakesh Iyer wrote:
> > > Hello Dmitry.
> > >
> > > Sorry for the wrap issue, my Outlook does not seem to obey the settings.
> > >
> > > I wanted to explain the tegra system resume path implementation so I can justify
> > > why I am doing this complicated fix and why I feel it will guarantee the resume
> > > is due to keypress.
> > >
> > > The tegra wake resume code is registered as a syscore ops.
> > > When the system is resumed due to a wake event, the suspend_enter (after wakeup)
> > > routine will invoke the tegra syscoreops_resume method and that routine will propagate
> > > the wake event to the individual ISR's through genirq.
> > > If kbc was wake source, kbc_isr will be invoked in this execution path.
> > >
> > > If system is resumed due to other reason, the tegra_syscoreops_resume code will not
> > > find the event.
> >
> > Consider the following sequence:
> >
> > 1. Something other than keyboard generates wakeup event
> > 2. It's IRQ fires up and gets serviced
> At this point syscoreops_resume has finished all its wakeup processing.
> > 3. System starts resuming devices
> > 4. User presses a key on the keypad while it is still suspended _and_
> >    registered as a wakeup source
> This will have no impact on the system and keypad ISR will not be
> invoked.
> > 5. Keypad's ISR runs as well and you decide that KEY_POWER should be
> >    reported even though keypad wasn't the real reason the system
> >    woke up.
> The interrupt line we use to detect wakeup processing is the keypress
> interrupt which is disabled and will never cause the ISR invocation from
> a device interrupt(i.e. the PIC).
> In other words KBC isr gets invoked for 2 reasons
> a) FIFO interrupt is generated, which will not happen as long as
> scanning logic is disabled until kbc_resume executes.
> b) The syscoreops_resume codepath calls into the ISR after finding KBC
> was a wakesource. If this happens it will happen only when the kernel
> resumes from its suspend code path.

>> Is this code already in mainline or still somewhere else?
I think this code has not made it to mainline yet. 
Its in the Android and ChromeOs kernel trees.

> >
> > Is this scenario not possible?
> >
> > Thanks.
> >
> With that being the case do you think the fix makes sense?

>> OK, yes. I do not think it is that important if we occasionally report
>> KEY_POWER even if KBC was not a true wakeup source but that's fine.


>> Dmitry

So can I assume this patch is accepted?

Thanks and Regards
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