3.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Aaron Lu <aaron.lu@xxxxxxxxx> 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 <qingshuai.tian@xxxxxxxxx> Tested-by: Aaron Lu <aaron.lu@xxxxxxxxx> # on "Idealpad u330p" Reported-and-tested-by: <erno@xxxxxx> # on "Acer Aspire V5-573G" Reported-and-tested-by: Kirill Tkhai <tkhai@xxxxxxxxx> # on "HP 250 G1" Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxx> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/acpi/video.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/acpi/video.c +++ b/drivers/acpi/video.c @@ -832,7 +832,7 @@ acpi_video_init_brightness(struct acpi_v 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; } -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html