linux-kernel - Re: Laptop shock detection and harddisk protection

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Message-ID: <20080817194838.GC4043@ucw.cz>
Date:	Sun, 17 Aug 2008 21:48:38 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	Shem Multinymous <multinymous@...il.com>,
	Elias Oltmanns <eo@...ensachen.de>,
	Thomas Renninger <trenn@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	IDE/ATA development list <linux-ide@...r.kernel.org>
Subject: Re: Laptop shock detection and harddisk protection

Hi!

> >> 2. If we're gonna unify interface, how much can we unify the backend?
> >>   Some devices are based on polling, others interrupt.  For polling,
> >>   is it better to delegate the whole polling to userland or is it
> >>   better to do some of it in kernel (tp_smapi seems to be doing
> >>   this)?
> > 
> > The ThinkPad accelerometer needs to be polled at very regular
> > intervals (max jitter on the order of 10ms), which sounds like a job
> > for the kernel.
> 
> Yes, I agree.
> 
> > This is because in ThinkPads we actually have a 4-level pile:
> > [hdapsd userspace] -> [hdaps kernel] -> [embedded controller] ->
> > [accelerometer A2D]
> > What the kernel polls is actually is the H8S embedded controller (EC)
> > chip, which in turn does its own polling of the accelerometer A2D.
> > Now, the EC has a tiny buffer and strange buffering semantics, and it
> > has its own internal clock, so the software->EC polling should be very
> > regular to minmize EC buffer overflows/underruns.
> 
> So, I think the whole polling should be implemented inside the kernel
> and the kernel should notify userland when new data is available,
> which is about what the current joystick implementation does and can
> be achieved using sysfs_notify_event().

I like joystick/input interface slightly better. In some cases,
machines with accelerometers (openmoko) use them for input primarily.

HP interface will be more specialized (but less useful); still  userland daemon can handle the differences...

							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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