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

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Date:	Sun, 4 Dec 2011 17:18:17 -0800
From:	riyer <riyer@...dia.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.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.

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

Regards
Rakesh

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