linux-kernel - Re: [linux-pm] [RFC][PATCH] PM: Avoid losing wakeup events during suspend

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Date:	Sun, 20 Jun 2010 23:02:40 -0700 (PDT)
From:	David Brownell <david-b@...bell.net>
To:	markgross@...gnar.org, Alan Stern <stern@...land.harvard.edu>
Cc:	Neil Brown <neilb@...e.de>, linux-pm@...ts.linux-foundation.org,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	mark gross <640e9920@...il.com>
Subject: Re: [linux-pm] [RFC][PATCH] PM: Avoid losing wakeup events during suspend

--- On Sun, 6/20/10, David Brownell <david-b@...bell.net> wrote:

... in a sort of "aren't we asking the
wrong questions??" manner ... 

I suspect that
looking at the problem in terms of how to
coordinate subsystems (an abstraction which
is at best very ad-hoc today!) we would
end up with a cleaner model, which doesn't
bother so many folk the ay wakelocks or
even suspend blockers seem to bother them...

> From: David Brownell <david-b@...bell.net>
> Subject: Re: [linux-pm] [RFC][PATCH] PM: Avoid losing wakeup events during suspend
> To: markgross@...gnar.org, "Alan Stern" <stern@...land.harvard.edu>
> Cc: "Neil Brown" <neilb@...e.de>, linux-pm@...ts.linux-foundation.org, "Dmitry Torokhov" <dmitry.torokhov@...il.com>, "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>, "mark gross" <640e9920@...il.com>
> Date: Sunday, June 20, 2010, 9:04 PM
> 
> > > > Indeed, the same problem arises if the
> event
> > isn't delivered to
> > > > userspace until after userspace is frozen.
> 
> Can we put this more directly:  the problem is
> that the *SYSTEM ISN'T FULLY SUSPENDED* when the
> hardware wake event triggers?  (Where "*SYSTEM*
> includes userspace not just kernel.  In fact the
> overall system is built from many subsystems,
> some in the kernel and some in userspace.
> 
> At the risk of being prematurely general:  I'd
> point out that these subsystems probably have
> sequencing requirements.  kernel-then-user is
> a degenerate case, and surely oversimplified.
> There are other examples, e.g. between kernel
> subsystems...  Like needing to suspend a PMIC
> before the bus it uses, where that bus uses
> a task to manage request/response protocols.
> (Think I2C or SPI.)
> 
> This is like the __init/__exit sequencing mess...
> 
> In terms of userspace event delivery, I'd say
> it's a bug in the event mechanism if taking the
> next step in suspension drops any event.  It
> should be queued, not lost...  As a rule the
> hardware queuing works (transparently)...
> 
> > Of course, the underlying
> > > > issue here is that the kernel has no direct
> way
> > to know when userspace
> > > > has finished processing an event.
> 
> 
> Again said more directly:  there's no current
> mechanism to coordinate subsystems.  Userspace
> can't communicate "I'm ready" to kernel, and
> vice versa.  (a few decades ago, APM could do
> that ... we dropped such mechanisms though, and
> I'm fairly sure APM's implementation was holey.)
> 
> 
> 
> 
> _______________________________________________
> linux-pm mailing list
> linux-pm@...ts.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/linux-pm
> 

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