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

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Message-Id: <1247644518.26272.88.camel@rzhang-dt>
Date:	Wed, 15 Jul 2009 15:55:18 +0800
From:	Zhang Rui <rui.zhang@...el.com>
To:	Richard Purdie <rpurdie@...ys.net>
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 Tue, 2009-07-14 at 20:29 +0800, Richard Purdie wrote:
> On Mon, 2009-07-13 at 21:41 +0100, Matthew Garrett wrote:
> > Certain hardware will send us events when the backlight brightness
> > changes. Add a function to update the value in the core, and
> > additionally send a uevent so that userspace can pop up appropriate
> > UI. The uevents are flagged depending on whether the update originated
> > in the kernel or from userspace, making it easier to only display UI
> > at the appropriate time.
> 
> This looks good and I like the idea. 
> 
> My main concern is that we don't start getting bug reports of 'missing'
> events and have clearly defined expectations of when we see what kind of
> events. For example, should an event be emitted when low battery causes
> the backlight to be limited? How about console blanking events turning
> off the backlight? Are there any other occasions we should be emitting
> change events and do we need to audit other drivers?
> 
> I did look to see if we could integrate this more into the backlight
> core but that doesn't look to be possible unfortunately, at least not
> without changing the drivers which these patches start.
> 
> Also, are "userspace" and "kernel" as meaningful as they could be? Would
> "sysfs" and "hwkeys" make more sense and allow for other future hardware
> differences? Perhaps someone will tie the backlight to an ambient light
> sensor for example...
> 

Hah, I just finished a patch to introduce the ACPI als driver.

I'm not quite familiar with the status of ALS support in Linux kernel.
and here is my questions,
I don't think we have a generic sysfs driver for ALS, i.e. ALS class
device, right?
do you guys think it's reasonable to have one?

thanks,
rui

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