linux-kernel - Re: [PATCH 0/3] Generic sysfs support for ACPI ALS and other ALS devices

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Date:	Thu, 06 Aug 2009 09:41:19 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Pavel Machek <pavel@....cz>
Cc:	linux-acpi <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	Richard Purdie <rpurdie@...ys.net>,
	Matthew Garrett <mjg59@...f.ucam.org>, Greg KH <greg@...ah.com>
Subject: Re: [PATCH 0/3] Generic sysfs support for ACPI ALS and other ALS
	devices

On Thu, 2009-08-06 at 00:19 +0800, Pavel Machek wrote:
> On Wed 2009-08-05 09:02:50, Zhang Rui wrote:
> > On Tue, 2009-08-04 at 21:21 +0800, Pavel Machek wrote:
> > > On Mon 2009-08-03 17:10:57, Zhang Rui wrote:
> > > > Hi, all,
> > > > 
> > > > This is the patch set I made to introduce ACPI ALS device driver
> > > > and a generic sysfs I/F for all the ALS devices, like ACPI ALS,
> > > > platform ALS, etc.
> > > > 
> > > > Patch 01 introduces the ACPI ALS device driver.
> > > > 
> > > > Patch 02 introduces ALS sysfs class.
> > > > 	Two sysfs I/F are created for each ALS device.
> > > >   /sys/class/als/alsX/illuminance:
> > > > 	the amount of light incident upon a specified surface area.
> > > >   /sys/class/als/alsX/mappings:
> > > > 	ambient light illuminance to display luminance mappings
> > > > 	that can be used by an OS to calibrate its ambient light policy
> > > > 	this is what I got on a test box:
> > > > 	cat /sys/class/als/als0/mappings
> > > > 	???Illuminance	Adjustment
> > > > 	          0	       70
> > > > 	         10	       73
> > > > 	         80	       85
> > > > 	        300	      100
> > > > 	       1000	      150
> > > 
> > > There's one value per file for sysfs... You should definitely have the
> > > header. 
> > > 
> > > Is there chance to already return adjusted values, avoiding this
> > > uglyness?
> > 
> > No,
> > For a ALS policy, user space should set a brightness level as the base
> > point, i.e. the backlight when display adjustment is 100.
> > and then uses the adjustment values gotten from this mappings to
> > calculate the actual brightness level the display should be put in.
> 
> Ok, so just make the code return only the "adjustement" -- userspace
> does not really need to know "illuminance" and you can do the mapping
> in the kernel AFAICT.
> 			

ALS exports
1. the current ambient light illuminance
2. the mappings

Backlight device exports
1. the brightness levels.

User space needs to:
1. set a brightness level as the base point
2. read the current ambient light illuminance from ALS device
3. read the ambient light illuminance to display adjustment mappings
4. calculate a proper brightness level we should set.

For example, if we set brightness 6 as the default brightness, i.e. the
brightness level when ambient light illuminance is 300.
Now we walk outdoors, and the current illuminance is 1000,
then we should set the new_brightness_level to (6 * 150%)

thanks,
rui

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