linux-kernel - Re: KMS Framebuffer on Intel N2600 (GMA3600)

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Date:	Wed, 14 Nov 2012 16:48:47 +0000 (UTC)
From:	Forconi <forconi@...ecomm.it>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: KMS Framebuffer on Intel N2600 (GMA3600)

Hi Alan,
first of all, thanks for your support.

> So the panel backlight register is set to indicate that the
> brightness
> will be handled by the firmware in some other way and not by the
> graphics.
> Do you have ACPI backlight support in your kernel ? Do you have the
> LVDS
> panel enabled in the BIOS ?

This backlight problem appears only when I run linux with KMS framebuffer,
when I run linux without KMS framebuffer, the backlight is always on.

Yes, I have ACPI enabled and ACPI backlight enabled, but running:
echo 100 > /sys/class/backlight/psb-bl/brightness
won't change anything.
In the BIOS there isn't any section relative to Video or LVDS settings.

But, in the end, this means that the driver si correctly loaded and the 
framebuffer is running but the panel backlight is off?
In other words, I can't see anything only because the backlight is off?

> It could be the value hasn't been initialised when it should have
> been,
> it could be your hardware has some other interface for this.
> 
> If you look at cdv_device.c you'll see cdv_get_max_backlight() checks
> for
> this case. If you can find out what the value should be then you can
> substitute
> 
>         if (max == 0) {
>                 DRM_DEBUG_KMS("LVDS Panel PWM value is 0!\n");
>                 /* i915 does this, I believe which means that we
>                 should
>                  * smash PWM control as firmware will take control of
>                  it.
>         	return 1;
>         }
> 
> 
> with
> 	if (max == 0)
> 		max = max_value << 16;
> 
> and test that case. If that doesn't work then probably the backlight
> is
> wired some other way. If ACPI handles it you may be able to handle it
> that way. If it's a custom driver interface in Windows you may have a
> problem.
> 
> Alan
> 

I don't know which could be the maximum value, there are any standard values
for backlight settings? I could try setting some values and see what happens...

Thanks again for your help.

Regards,
Samuele.

-- 
Ing. Samuele Forconi
Responsabile Sviluppo SW
WaveComm S.r.l.
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