linux-kernel - Re: hp accelerometer: add freefall detection

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Date:	Fri, 13 Feb 2009 13:28:29 +0100
From:	Pavel Machek <pavel@....cz>
To:	?ric Piel <eric.piel@...mplin-utc.net>
Cc:	akpm@...ux-foundation.org, LKML <linux-kernel@...r.kernel.org>,
	trenn@...e.de, vbotka@...e.cz, jikos@...e.cz
Subject: Re: hp accelerometer: add freefall detection

> From: Pavel Machek <pavel@...e.cz>
> > 
> > This adds freefall handling to hp_accel driver.  According to HP, it
> > should just work, without us having to set the chip up by hand.
> > 
> > hpfall.c is example .c program that parks the disk when accelerometer
> > detects free fall.  It should work; for now, it uses fixed 20seconds
> > protection period.
> > 
> > Signed-off-by: Pavel Machek <pavel@...e.cz>
> > Cc: Thomas Renninger <trenn@...e.de>
> > Cc: ???ric Piel <eric.piel@...mplin-utc.net>
> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Hi Pavel,
> Sorry for being amazingly late, reading the latest patches from
> Giuseppe, I noticed some parts in this patch which are strange.
> Basically you scrap all the init and all the poweroff. Some of the
> things there were put for some purpose, and I wonder if you've verified
> everything keeps working correctly.

Yes; HP tells me I do not need to touch the hardware, and in my tests
touching the hardware actually broke the stuff. Yes, position and
freefall detection still worked without manually touching the hw.

Unfortunately, I don't have the hardware any more...

> > @@ -110,26 +114,13 @@ static void lis3lv02d_get_xyz(acpi_handl
> >  void lis3lv02d_poweroff(acpi_handle handle)
> >  {
> >  	adev.is_on = 0;
> > -	/* disable X,Y,Z axis and power down */
> > -	adev.write(handle, CTRL_REG1, 0x00);
> So we are not turning off the device on poweroff()?! Why? Did you notice
> problems when we were doing it?

Well, HP told me not to touch the hardware, so I'm not touching it.

> Actually I've always wondered if it was worthy to turn it off because
> I've never been able to measure a difference in power consumption. Have
> you done the measurement and noticed there is no effect? I'd be glad we
> can get rid of this power management thing, but then we can scratch much
> more than just this line!

Well,  if you can't measure the difference, it is probably not worth
doing ... for HP notebooks anyway.

> > -	/*
> > -	 * BDU: LSB and MSB values are not updated until both have been read.
> > -	 *      So the value read will always be correct.
> > -	 * IEN: Interrupt for free-fall and DD, not for data-ready.
> > -	 */
> > -	adev.read(handle, CTRL_REG2, &val);
> > -	val |= CTRL2_BDU | CTRL2_IEN;
> > -	adev.write(handle, CTRL_REG2, val);
> This part is rather scary. Did you read the comment? If you don't
> activate BDU you cannot be sure that the data you read is valid. I see
> no reason why this would interfere with the free-fall detection so
> unless you have a really good case, let's keep it. On the other hand, I
> don't mind removing IEN if you've noticed that it's not useful or
> interfering.

Well, I just removed all the writes at once and notice it
helped... And HP tells me I don't need to touch the hardware...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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