linux-kernel - Re: [PATCH] lis3lv02d: add axes knowledge of HP Pavilion dv5 models

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Date:	Wed, 11 Feb 2009 00:34:34 +0100
From:	Éric Piel <Eric.Piel@...mplin-utc.net>
To:	Giuseppe Bilotta <giuseppe.bilotta@...il.com>
Cc:	Pavel Machek <pavel@...e.cz>, linux-kernel@...r.kernel.org,
	Palatis Tseng <palatis@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] lis3lv02d: add axes knowledge of HP Pavilion dv5 models

Giuseppe Bilotta schreef:
> On Tue, Feb 10, 2009 at 10:39 PM, Giuseppe Bilotta
> <giuseppe.bilotta@...il.com> wrote:
>> On Tue, Feb 10, 2009 at 11:10 AM, Pavel Machek <pavel@...e.cz> wrote:
>>> Yeah, that patch. Not sure what to do next... you could grab lis3
>>> manual and see if you can setup chip by hand to get better results...
>> As Eric pointed out, it looks definitely like an endianness problem,
>> although there are a few strange things which are happening at the
>> same time. Is the lis3 manual available online somewhere, or can I
>> request it to the mfgr?
> 
> 'k, found it on the STMicroelectronics website. Reading the doc about
> LIS3LV02DL I see that WHO_AM_I should return 3Ah, but my sensor
> returns 3Bh. I'll see if I find the correct datasheet for this one
> instead, it might have info about the differences.
Ah, yes, that would explain a lots of things! Your chip is 8bits! The 
original reporter had not reported anything and I didn't pay attention 
to this "little" detail when comparing the specs.


> One thing that I noticed is that (modulo axis inversion) I'm able to
> use the sensor correctly if I set the thing to only use the high byte,
> totally discarding the lower byte:
> 	return *((s8*)(&hi));
> Maybe this sensor needs a different setup to return 12 instead of 8
> bits of information.
So you either have the lis302dl or the lis202dl (2 axes only):
http://www.st.com/stonline/products/literature/ds/12726/lis302dl.htm
http://www.st.com/stonline/products/literature/ds/13624/lis202dl.htm

I'd guess you have the one with 3 axes as all the axes had changing 
values. More optimistically I'll imagine that no HP laptop has the 2D 
chip, which unfortunately share the same who_am_i value.

So to get it working you need to change the lis3lv02d_read_16() function 
to only read the low byte and put the high byte to FFh if the high bit 
(80h) is set (I guess it's a signed integer). Then for completeness you 
need to put MDPS_MAX_VAL to 128.

Does it work?

Once this is verified, you should add a flag in the driver for the 
device to know whether it's 8bits or 12bits. This would be set at 
initialization according to the who_am_i value.

Eric
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