Re: [PATCH 2/2] ACPI / video: Quirk initial backlight level 0

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

On 11/07/2013 06:04 AM, Rafael J. Wysocki wrote:
> On Wednesday, November 06, 2013 09:07:10 AM Aaron Lu wrote:
>> Some firmware doesn't initialize initial backlight level to a proper
>> value and _BQC will return 0 on first time evaluation. We used to be
>> able to detect such incorrect value with our code logic, as value 0
>> normally isn't a valid value in _BCL. But with the introduction of Win8,
>> firmware begins to fill _BCL with values from 0 to 100, now 0 becomes
>> a valid value but that value will make user's screen black. This patch
>> test initial _BQC for value 0, if such a value is returned, do not use
>> it.
>>
>> Reference: https://bugzilla.kernel.org/show_bug.cgi?id=64031
>> Reference: https://bugzilla.kernel.org/show_bug.cgi?id=61231
>> Reference: https://bugzilla.kernel.org/show_bug.cgi?id=63111
>> Reported-by: Qingshuai Tian <qingshuai.tian@intel.com>
>> Tested-by: Aaron Lu <aaron.lu@intel.com> on "Idealpad u330p"
>> Reported-and-tested-by: <erno@iki.fi> on "Acer Aspire V5-573G"
>> Reported-and-tested-by: Kirill Tkhai <tkhai@yandex.ru> on "HP 250 G1"
>> Signed-off-by: Aaron Lu <aaron.lu@intel.com>
>> Cc: stable <stable@vger.kernel.org>
> 
> All stable, or any particular series?

All stable.

Thanks,
Aaron

> 
>> ---
>>  drivers/acpi/video.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
>> index bf521b36c2f9..a049fa9360d0 100644
>> --- a/drivers/acpi/video.c
>> +++ b/drivers/acpi/video.c
>> @@ -858,7 +858,7 @@ acpi_video_init_brightness(struct acpi_video_device *device)
>>  		for (i = 2; i < br->count; i++)
>>  			if (level == br->levels[i])
>>  				break;
>> -		if (i == br->count)
>> +		if (i == br->count || !level)
>>  			level = max_level;
>>  	}
>>  
>>