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2c62333a40
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@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: All applicable <stable@vger.kernel.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>