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Subject: Re: [PATCH 0/3] Generic sysfs support for ACPI ALS and other ALS
	devices
From: Zhang Rui <rui.zhang@intel.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: linux-acpi <linux-acpi@vger.kernel.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Len Brown <lenb@kernel.org>, Richard Purdie <rpurdie@rpsys.net>,
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Date: Tue, 25 Aug 2009 09:13:40 +0800
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On Fri, 2009-08-21 at 19:51 +0800, Pavel Machek wrote:
> Hi!
> 
> > > > Could you please look at the documentation about ALS sysfs class in the
> > > > patch I sent out just now, and comment on that one please? thanks!
> > > 
> > > I did. The interface is too ugly to live.
> > 
> > Hi, Pavel,
> > 
> > I tried to convert the ALS sysfs I/F to two attributes only, i.e.
> > illuminance and adjustment.
> > But I found several potential problems.
> > 1. the illuminance to display adjustment mappings can not be convert to
> > a brightness level smoothly.
> > for example,
> > 	illuminance	adjustment
> > 1	600		70
> > 2	900		100
> > 3	1500		120
> > when the current illuminance is not one of the values listed in the
> > mappings, e.g. 750, the ALS driver don't have enough knowledge to get
> > the proper display adjustment, especially that a proper display
> > adjustment would be easy to select a proper brightness level.
> > We'd better leave this to user space, which is more flexible.
> 
> Well, what interpolation does ACPI specs suggest to do?

Well, the spec says that "Extrapolation of the values between
these points is OS-specific", and it uses a piecewise linear
approximation in an example.

>  Maybe it is
> easier to have linear interpolation in the kernel than to have ugly
> 20-file interface?

yes. we can do that.
refreshed patch will be sent out later.

thanks,
rui