From: Aaron Lu Date: Wed, 6 Nov 2013 01:07:10 +0000 (+0800) Subject: ACPI / video: Quirk initial backlight level 0 X-Git-Tag: v3.11.10~13 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=20979757d03ab714e48395dd9745ff7401920e96;p=thirdparty%2Fkernel%2Fstable.git ACPI / video: Quirk initial backlight level 0 commit 2c62333a408f5badd2d2ffd7177f95deeccc5ca4 upstream. 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. References: https://bugzilla.kernel.org/show_bug.cgi?id=64031 References: https://bugzilla.kernel.org/show_bug.cgi?id=61231 References: https://bugzilla.kernel.org/show_bug.cgi?id=63111 Reported-by: Qingshuai Tian Tested-by: Aaron Lu # on "Idealpad u330p" Reported-and-tested-by: # on "Acer Aspire V5-573G" Reported-and-tested-by: Kirill Tkhai # on "HP 250 G1" Signed-off-by: Aaron Lu Signed-off-by: Rafael J. Wysocki Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c index 3270d3c8ba4ed..28e5184b565b5 100644 --- a/drivers/acpi/video.c +++ b/drivers/acpi/video.c @@ -848,7 +848,7 @@ acpi_video_init_brightness(struct acpi_video_device *device) for (i = 2; i < br->count; i++) if (level_old == br->levels[i]) break; - if (i == br->count) + if (i == br->count || !level) level = max_level; }