linux-kernel - Re: [linux-pm] [PATCH] PM: Make it possible to avoid wakeup events from being lost

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 29 Jun 2010 15:57:24 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	David Brownell <david-b@...bell.net>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>, mark gross <640e9920@...il.com>,
	Neil Brown <neilb@...e.de>, <linux-pci@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	<Arve@...p1.linux-foundation.org>,
	Florian Mickler <florian@...kler.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	<linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH] PM: Make it possible to avoid wakeup events
 from being lost

On Mon, 28 Jun 2010, David Brownell wrote:

> Did someone post the canonical driver changes
> to make use of this?

No, not really.  The patch itself contains an example (PCI) but it 
doesn't demonstrate the full range of possible usages.

>  Something like
> 
>   suspend() { /* if wake-enabled, up count */ }
>   resume() { /* if upcounted, downcount */ }
> 
> is what first comes to mind.. expecting that
> the suspend/resume methods in the driver are
> already doing the right things for enabling
> and later disabling the "system wake" behavior
> on the various relevant hardware events...

The PCI example looks like this:

	resume()
	{
		...
		if (device_may_wakeup(dev))
			pm_wakeup_event(dev, TIMEOUT_GUESS);
		...
	}

where TIMEOUT_GUESS is an estimate of how long to wait before allowing 
the system to sleep.

For things like keyboards, an example would go more like this:

	irq_handler()
	{
		...
		if (key-press event occurred) {
			...
			if (input queue is empty)
				pm_stay_awake(dev);
			add event to input queue;
			...
		}
		...
	}

	read_queue()
	{
		...
		send queued data to userspace
		if (input queue is empty)
			pm_relax();
		...
	}

I left out the device_may_wakeup tests; things become rather 
complicated if you can have more than one keyboard feeding the same 
input queue and some of them are wakeup-enabled while others aren't.

Clearly the appropriate changes will depend on the subsystem and the
kind of event.  They may also end up depending on the platform; perhaps
this will be used only on relatively small systems like an Android
phone.

Alan Stern

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/