Re: [intel/acpi] backlight - T61

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Wednesday, December 03, 2008 3:14 pm Zhenyu Wang wrote:
> On 2008.12.01 13:08:23 +0800, Zhang Rui wrote:
> > > However, testing FC10 with the latest upstream kernel,
> > > including the i915 changes that appeared today...
> > > it seems that GUI mode forgets the brighness when
> > > I switch to console mode.  Eg. If I use /sys or
> > > hotkeys in GUI mode to reduce brightness to 0,
> > > it stays dim when I switch to console mode,
> > > but switches back to max brightness when
> > > I switch back to GUI mode.
> >
> > hah, that's a done by X.
> > ZhenYu pointed out that the graphics driver will set the backlight to
> > maximum if it is 0 when switching to GUI.
> > what if reducing the brightness to a lower but not 0 level?
> > it should switch back to the original value, right?
> > cc ZhenYU. :)
>
> This depends on the backlight control method used by Xorg
> video driver. We have this comment in the driver from Jesse I think,
>
>  /*
>   * If we're going from off->on we may need to turn on the backlight.
>   * We should use the saved value whenever possible, but on some
>   * machines 0 is a valid backlight value (due to an external backlight
>   * controller for example), so on them, when turning LVDS back on,
>   * they'll always re-maximize the brightness.
>   */
> if (!(INREG(PP_CONTROL) & POWER_TARGET_ON) &&
> 	dev_priv->backlight_duty_cycle == 0)
> 	dev_priv->backlight_duty_cycle = dev_priv->backlight_max;
>
> It looks if we're using kernel backlight method, '0' should be a human
> sensible dim level instead of meaningless near-to-black level, right?
>
> So how about this patch against current xf86-video-intel?
>
> ---
> diff --git a/src/i830_lvds.c b/src/i830_lvds.c
> index 239bc89..1799eab 100644
> --- a/src/i830_lvds.c
> +++ b/src/i830_lvds.c
> @@ -400,7 +400,8 @@ i830SetLVDSPanelPower(xf86OutputPtr output, Bool on)
>  	 * they'll always re-maximize the brightness.
>  	 */
>  	if (!(INREG(PP_CONTROL) & POWER_TARGET_ON) &&
> -	    dev_priv->backlight_duty_cycle == 0)
> +	    dev_priv->backlight_duty_cycle == 0 &&
> +	    pI830->backlight_control_method < BCM_KERNEL)
>  	    dev_priv->backlight_duty_cycle = dev_priv->backlight_max;
>
>  	OUTREG(PP_CONTROL, INREG(PP_CONTROL) | POWER_TARGET_ON);
> ---
>
> p.s Len, if for intel graphics specific issue, we have another
> intel-gfx@lists.freedesktop.org for such discuss. Thanks.

I'd be a little happier with a != BCM_KERNEL, but other than that it seems 
fine.

-- 
Jesse Barnes, Intel Open Source Technology Center

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