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    Subject[PATCH 3.10 22/80] ACPI / video: Quirk initial backlight level 0
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Aaron Lu <aaron.lu@intel.com>

    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@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>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/acpi/video.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/acpi/video.c
    +++ b/drivers/acpi/video.c
    @@ -846,7 +846,7 @@ 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;
    }




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