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

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Date:	Sun, 4 Dec 2011 20:27:36 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	riyer <riyer@...dia.com>
Cc:	"rydberg@...omail.se" <rydberg@...omail.se>,
	Stephen Warren <swarren@...dia.com>,
	Laxman Dewangan <ldewangan@...dia.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
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?

> > 
> > 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.

Thanks.

-- 
Dmitry
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