linux-kernel - Re: [PATCH 1/3] backlight: Allow drivers to update the core, and generate events on changes

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Date:	Wed, 15 Jul 2009 10:11:29 +0100
From:	Richard Purdie <rpurdie@...ys.net>
To:	Zhang Rui <rui.zhang@...el.com>
Cc:	Matthew Garrett <mjg@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"lenb@...nel.org" <lenb@...nel.org>,
	"corentincj@...aif.net" <corentincj@...aif.net>
Subject: Re: [PATCH 1/3] backlight: Allow drivers to update the core, and
	generate events on changes

On Wed, 2009-07-15 at 16:38 +0800, Zhang Rui wrote: 
> On Wed, 2009-07-15 at 16:22 +0800, Richard Purdie wrote:
> > We don't have one that I'm aware of.
> > 
> > The first question is what information and configuration options are we
> > likely to have with ALS sensors? If its just a light level reading, the
> > input subsystem is ideally suited for sharing that. Is there
> > configuration we need to expose?
> > 
> For an ACPI ALS device, only these two are mandatory
> 1. the current ambient light illuminance.
> 2. A list of luminance mappings, including the "display luminance
> adjustment" and "ambient light illuminance", which can be used by OS to
> determine the ambient light policy.

So there are basically two values we're ever interested in at a given
point in time. The current ambient light reading and the corresponding
display luminance adjustment. Both of those could just be exposed as an
input device really?

> IMO, the ALS driver should just export these info to user space, and we
> can do the display backlight adjustment in user space,
> via /sys/class/backlight.

Agreed, userspace should be where policy is decided. Having a standalone
module which connected the two together with a "default" policy might be
acceptable too though? If userspace then wants to handle things it just
makes sure the module is not loaded.

Cheers,

Richard

-- 
Richard Purdie
Intel Open Source Technology Centre

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