backlight support

backlight support

[sebastien.brennion-gM/Ye1E23mwN+BqQ9rBEUg]

Hi there,

A lot of people are experiencing problems with backlight support. It seems 
that they won't be any solution in near future, so I wanted to ask if nouveau 
is going to support the backlight management, and when ?

thx
sebastien

Re: backlight support

[Maarten Maathuis]

There is some support for laptop backlight control.

(http://cgit.freedesktop.org/nouveau/linux-2.6/tree/drivers/gpu/drm/nouveau/nouveau_backlight.c)

If you have older hw, then you may need to figure out how to control it.

I see only a few bug reports related to backlights, so a lot of people
seems like an overstatement.

Maarten.

Re: backlight support

[sebastien.brennion-gM/Ye1E23mwN+BqQ9rBEUg]

Thanks for your answer,


I use karmic, with the already packaged 0.0.14+git20090715-0ubuntu1 from 
nouveau...
I can't see any backlight information in /sys/class/backlight
Could you tell me how it is supposed to work with nouveau ? I though the 
driver would provide backlight information there??

I don't think to have a old hw, but I don't know what is old for devs... 
nVidia Corporation G86 [GeForce 8400M GT]

As I mentionned backlight problems, I didn't mean bug in relation with 
nouveau, but for example on nvnews, on launchpad, on ubuntu forums, I already 
spoken with a lot of people experiencing backlight problem with nvidia 
driver... I do not like so much overstatements ;)


Le Friday 24 July 2009 17:10:37, vous avez écrit :
> There is some support for laptop backlight control.
>
> (http://cgit.freedesktop.org/nouveau/linux-2.6/tree/drivers/gpu/drm/nouveau
>/nouveau_backlight.c)
>
> If you have older hw, then you may need to figure out how to control it.
>
> I see only a few bug reports related to backlights, so a lot of people
> seems like an overstatement.
>
> Maarten.

Re: backlight support

[Pekka Paalanen]

On Mon, 27 Jul 2009 18:46:36 +0200
sebastien.brennion-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org wrote:

> I use karmic, with the already packaged 0.0.14+git20090715-0ubuntu1 from 
> nouveau...

Does that build have backlight support enabled?
It was made configurable a day before that package date in
http://cgit.freedesktop.org/nouveau/linux-2.6/commit/?id=4df79d74cf77cad4c27348b3299fb6e046883105

> I can't see any backlight information in /sys/class/backlight
> Could you tell me how it is supposed to work with nouveau ? I though the 
> driver would provide backlight information there??
> 
> I don't think to have a old hw, but I don't know what is old for devs... 
> nVidia Corporation G86 [GeForce 8400M GT]

That is considered quite new.

-- 
Pekka Paalanen
http://www.iki.fi/pq/

Re: backlight support

[schmirrwurst-gM/Ye1E23mwN+BqQ9rBEUg]

I've tried with the ppa version that is git+20090724+094e4e0
but still no backlight information on /proc/acpi/video and 
/sys/class/backlight...

Le Monday 27 July 2009 19:00:46, Pekka Paalanen a écrit :
> On Mon, 27 Jul 2009 18:46:36 +0200
>
> sebastien.brennion-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org wrote:
> > I use karmic, with the already packaged 0.0.14+git20090715-0ubuntu1 from
> > nouveau...
>
> Does that build have backlight support enabled?
> It was made configurable a day before that package date in
> http://cgit.freedesktop.org/nouveau/linux-2.6/commit/?id=4df79d74cf77cad4c2
>7348b3299fb6e046883105
>
> > I can't see any backlight information in /sys/class/backlight
> > Could you tell me how it is supposed to work with nouveau ? I though the
> > driver would provide backlight information there??
> >
> > I don't think to have a old hw, but I don't know what is old for devs...
> > nVidia Corporation G86 [GeForce 8400M GT]
>
> That is considered quite new.

Re: Backlight support

[Richard Purdie]

John Lenz:
> Perhaps the patch being referred to is the "Backlight and LCD module
> patches" that Andrew Zabolotny and I proposed on lkml?

I think the above patch was nearly there. The issues seemed to be with the
method of associating framebuffer devices with their backlights. I've come
up with a solution to that problem (see below) so that code can be removed
from that patch and that should make it acceptable for mainstream kernel
inclusion.

Russ Dill:
> The driver/bus/device model driver? Probably just no one there with
> the time to spend on it. It be a real help, and would be a good use of
> sysfs (for changing contrast, getting info, etc).

I'm keen to get this sorted out and I agree its an ideal use of sysfs. I'm
still getting up to speed on sysfs though...

Steven Scholz:
> Where can I find the most recent version of your patch?

I've had a discussion with Andrew. I think he's going to find the latest
version of the and post it for inclusion without the problematic parts...
Andrew?

> Excuse me ignorance, but what is "frontlight"?

I think a frontlight shines onto the display and reflects off a reflector at
the back of the LCD. A backlight lights it from the rear. As far as the
sysfs representations go, they'll be essentially identical. You can read a
frontlit display without the light in strong light. The backlit display
always needs the backlight.

My solution for associating backlight drivers with framebuffer drivers is
for the backlight driver to call fb_register_client() and register for fb
events. You can then intercept blanking requests (FB_EVENT_BLANK) which get
passed with an fb_info struct and the new blanking setting. It's entirely up
to the backlight driver how it tells which displays it should be blanking.
For something like my PDA, there is only one framebuffer/LCD to blank but in
other cases you would analyse fb_info. (FB_EVENT_BLANK is destined for
2.6.11)

I propose this discussion should move to linux-fbdev-devel and hopefully
Andrew will provide a sysfs representation we can discuss (maybe with some
comments from lkml).

I have one implementation question though - should backlight drivers be in
the arch folder (arch/arm/mach-pxa in my case) or should
drivers/video/backlights be created? They're all likely to be using
fb_register_client() so maybe the latter would be preferred?

Richard



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Re: Backlight support

[Nicolas Pitre]

On Tue, 30 Nov 2004, Richard Purdie wrote:

> I have one implementation question though - should backlight drivers be in
> the arch folder (arch/arm/mach-pxa in my case) or should
> drivers/video/backlights be created? They're all likely to be using
> fb_register_client() so maybe the latter would be preferred?

Try to keep pieces of code sorted on their function first. It is harder 
for a subsystem maintainer to go all over the tree looking for all files 
that a particular change to the subsystem might affect than it is for an 
architecture maintainer to look after files affecting a specific 
architecture.


Nicolas

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Re: Backlight support

[Russ Dill]

> I'm keen to get this sorted out and I agree its an ideal use of sysfs. I'm
> still getting up to speed on sysfs though...
>

The sysfs interface should probably tell you about the backlight too,
like, does it need to be on, or is ambient light enough. Possibly
recommended power modes, standardized power modes, or recommendations
based on ambient light.

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