Re: [PATCH 3/6] [-mm]: ACPI: duplicate ACPI sleep "alarm" attribute in sysfs

From: Len Brown <lenb@kernel.org>
To: linux-pm@lists.osdl.org
Cc: "linux-acpi@vger" <linux-acpi@vger.kernel.org>,
	Alessandro Zummo <alessandro.zummo@towertech.it>,
	Paul Sokolovsky <pmiscml@gmail.com>, Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH 3/6] [-mm]: ACPI: duplicate ACPI sleep "alarm" attribute in	sysfs
Date: Wed, 24 Jan 2007 23:21:09 -0500	[thread overview]
Message-ID: <200701242321.09850.lenb@kernel.org> (raw)
In-Reply-To: <200701071944.59470.david-b@pacbell.net>

On Sunday 07 January 2007 22:44, David Brownell wrote:
> On Sunday 07 January 2007 3:19 am, Pavel Machek wrote:
> > 
> > > Create /sys/power/alarm.
> > > The way it works is exactly the same as /proc/acpi/alarm.
> > > I.e. "#echo yyyy-mm-dd hh-mm-ss >/sys/power/alarm" supports existing absolute time.
> > > And "#echo +yyyy-mm-dd hh-mm-ss >/sys/power/alarm" supports a duration.
> > 
> > NAK. /proc/acpi/alarm is a mess, and this just moves it to /sysfs.
> > 'One value per file', please.
> 
> Sort of like the appended patch, instead ... which doesn't need to know a
> thing about ACPI.  This is what I suggested in response to an earlier patch
> from Paul Sokolovsky.
> 
> - Dave
> 
> 
> ================	CUT HERE
> This adds a new "wakealarm" sysfs attribute to RTC class devices which
> support alarm operations and are wakeup-capable:
> 
>  - It reads as either empty, or the scheduled alarm time as seconds
>    since the POSIX epoch.  (That time may already have passed, since
>    nothing currently enforces one-shot alarm semantics...)
> 
>  - It can be written with an alarm time in the future, again seconds
>    since the POSIX epoch, which enables the alarm.
> 
>  - It can be written with an alarm time not in the future (such as 0,
>    the start of the POSIX epoch) to disable the alarm.
> 
> Usage examples, after "cd /sys/class/rtc/rtcN":
> 
>     alarm after 45 minutes:
> 	# echo $(( $(cat since_epoch) + 45 * 60 )) > wakealarm
>     alarm next tuesday evening (using GNU date):
> 	# date -d '10pm tuesday' "+%s" > wakealarm
>     disable alarm:
>     	# echo 0 > wakealarm
> 
> This resembles the /proc/acpi/alarm file in that nothing happens when
> the alarm triggers ... except possibly waking the system from sleep.
> It's also like that in a nasty way:  not much can be done to prevent
> one task from clobbering another task's alarm settings.
> 
> It differs from that file in that there's no in-kernel date parser.
> 
> Note that a few RTCs ignore rtc_wkalrm.enabled when setting alarms, or
> aren't set up correctly, so they won't yet behave with this attribute.
> 
> Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

How do I ask to wake up "as soon as possible"?

This is what a box that is testing suspend-resume would want to do.

thanks,
-Len