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

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Thursday, September 25, 2014 11:15:35 AM 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:
> 
> 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;
> +}

Well, what about

	return acpi_video_backlight_support() && !acpi_video_verify_backlight_support();

?

> +
>  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;
>  	}
> --
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-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.