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 16:47:10 +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 15:13 +0800, Pavel Machek wrote:
> > > > 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%)
> 
> Yes, so just export
> 
> ALS exports
> 1. the current ambient light illuminance
> 2. the current mapped ambient light illuminance
> 
In fact, only one attribute is enough.
The ALS driver can query the current illuminance, parse the mapping and
only export the display luminance adjustment values to user space.

> Backlight device exports
> 1. the brightness levels.
>  
> User space needs to:
> 1. set a brightness level as the base point
> 2. read the current mapped ambient light illuminance from ALS device
> 3. calculate a proper brightness level we should set.
> 
then user space just needs to
1. set a brightness level as the base point
2. get the display adjustment value and calculate a proper brightness
level at any time.

this is easier, but it makes me feel that this doesn't look like an
_ALS_ device any more.
We still should export some ALS properties to user space, shouldn't we?

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!

thanks,
rui


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