Re: ACPI/i915: Cannot configure display brightness on Dell Latitude E6440

["Pali Rohár" <pali.rohar@gmail.com>]

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On Thursday 25 September 2014 05:15:35 Aaron Lu wrote:
> Hi Hans,
> 
> Thanks for following up and explaining the situation to Pali.
> 
> On 09/25/2014 02:21 AM, Pali Rohár wrote:
> > On Wednesday 24 September 2014 16:34:21 Hans de Goede wrote:
> >> Ok, so the dell-laptop interface is just an obsolete
> >> wrapper around the i915 opregion code, which shows that
> >> the right interface to use is the i915 one, which we do if
> >> you don't specify any kernel commandline parameters, case
> >> closed.
> >> 
> >> Regards,
> >> 
> >> Hans
> > 
> > Nope, its not closed.
> > 
> > Still i915 interface has problem with setting backlight. It
> > exports lot of levels which turning display off. Which
> > breaking exiting applications for configuring display
> > brightness. This is still big regression as black screen is
> > not want people want to see.
> > 
> > Driver dell-laptop has exported only few - not thousands
> > level (which is insane) and only usefull levels (not lot of
> > levels which turn display off).
> > 
> > So for this reason using i915 backlight interface is not
> > possible and also Dell (for E6440) set kernel param
> > acpi_backlight=vendor to use dell_laptop module for
> > controlling brightness.
> > 
> > On my laptop E6440 is better for using dell-laptop and not
> > acpi or i915.
> 
> Hi Pali,
> 
> Please test this patch:
> 

Hi! this patch fixing this problem. With acpi_backlight=vendor 
dell-laptop will register backlight interface which is working 
again. Also userspace application dellLcdBrightness is working 
now without problem.

Can you going to send this patch also to stable 3.16 branch? As 
it fixing commit 0b9f7d93ca6109048a4eb06332b666b6e29df4fe.

> diff --git a/drivers/gpu/drm/i915/intel_opregion.c
> b/drivers/gpu/drm/i915/intel_opregion.c index
> ca52ad2ae7d1..15534345bd57 100644
> --- a/drivers/gpu/drm/i915/intel_opregion.c
> +++ b/drivers/gpu/drm/i915/intel_opregion.c
> @@ -396,6 +396,24 @@ int intel_opregion_notify_adapter(struct
> drm_device *dev, pci_power_t state) return -EINVAL;
>  }
> 
> +/*
> + * Some of the Thinkpads' firmware will issue a backlight
> change operation + * region request unconditionally on AC
> plug/unplug, this is undesirable and + * should be ignored.
> Then there is a Dell laptop whose vendor backlight + *
> interface also makes use of operation region request to
> change backlight + * level and we have to keep it work. The
> rule used here is: if the vendor + * backlight interface is
> not in use and the ACPI backlight interface is + * broken, we
> ignore the requests; oterwise, we keep processing them. + */
> +static bool should_ignore_backlight_request(void)
> +{
> +	if (acpi_video_backlight_support() &&
> +	    !acpi_video_verify_backlight_support())
> +		return true;
> +
> +	return false;
> +}
> +
>  static u32 asle_set_backlight(struct drm_device *dev, u32
> bclp) {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> @@ -404,11 +422,7 @@ static u32 asle_set_backlight(struct
> drm_device *dev, u32 bclp)
> 
>  	DRM_DEBUG_DRIVER("bclp = 0x%08x\n", bclp);
> 
> -	/*
> -	 * If the acpi_video interface is not supposed to be used,
> don't -	 * bother processing backlight level change requests
> from firmware. -	 */
> -	if (!acpi_video_verify_backlight_support()) {
> +	if (should_ignore_backlight_request()) {
>  		DRM_DEBUG_KMS("opregion backlight request ignored\n");
>  		return 0;
>  	}

-- 
Pali Rohár
pali.rohar@gmail.com

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