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

[Aaron Lu <aaron.lu@intel.com>]

On 09/26/2014 03:58 AM, Rafael J. Wysocki wrote:
> 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();
> 
> ?

Yes that's better.
Will send out a patch with this change, thanks for the suggestion.

-Aaron

> 
>> +
>>  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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>