linux-kernel - Re: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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Date:	Wed, 2 Jun 2010 19:44:59 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Florian Mickler <florian@...kler.org>, Neil Brown <neilb@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul@...p1.linux-foundation.org" <Paul@...p1.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Bottomley <James.Bottomley@...e.de>
Subject: Re: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8] 
	Suspend block api (version 8)

On Wed, Jun 2, 2010 at 4:32 PM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
> On Wed, Jun 02, 2010 at 09:05:21PM +0200, Florian Mickler wrote:
>> On Wed, 2 Jun 2010 21:02:24 +1000
>> Neil Brown <neilb@...e.de> wrote:
>> >
>> > And this decision (to block suspend) really needs to be made in the driver,
>> > not in userspace?
>>
>> Well, it fits. The requirement is a direct consequence of the intimate
>> knowledge the driver has about the driven devices.
>
> That is not really true. A driver does have intimate knowledge of the
> device, however it does not necessarily have an idea about the data read
> from the device. Consider the gpio_matrix driver: Arve says that it has
> to continue scanning matrix once first interrupt arrvies. But it really
> depends on what key has been pressed - if user pressed KEY_SUSPEND or
> KEY_POWER it cmight be better if we did not wait for key release but
> initiated the action right away. The decision on how system reacts to a
> key press does not belong to the driver but really to userspace.

If we just suspend while the keypad scan is active, a second press of
KEY_POWER would not be able wake the device up. The gpio keypad matrix
driver has two operating modes. No keys are pressed: all the outputs
are active so a key press will generate an interrupt in one of the
inputs. Keys are pressed: Activate a single output at a time so we can
determine which keys are pressed. The second mode is entered when the
driver gets an interrupt in the first mode. The first mode is entered
if the scan detected that no keys are pressed. The driver could be
modified to stop the scan on suspend and forcibly put the device back
in no-keys-pressed state, but pressing additional keys connected to
the same input can no longer generate any events (the input does not
change).

-- 
Arve Hjønnevåg
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