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    Subject[PATCH 3.10 64/97] ACPI / video: Filter the _BCL table for duplicate brightness values
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

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

    From: Hans de Goede <hdegoede@redhat.com>

    commit bd8ba20597f0cfef3ef65c3fd2aa92ab23d4c8e1 upstream.

    Some devices have duplicate entries in there brightness levels table, ie
    on my Dell Latitude E6430 the table looks like this:

    [ 3.686060] acpi backlight index 0, val 80
    [ 3.686095] acpi backlight index 1, val 50
    [ 3.686122] acpi backlight index 2, val 5
    [ 3.686147] acpi backlight index 3, val 5
    [ 3.686172] acpi backlight index 4, val 5
    [ 3.686197] acpi backlight index 5, val 5
    [ 3.686223] acpi backlight index 6, val 5
    [ 3.686248] acpi backlight index 7, val 5
    [ 3.686273] acpi backlight index 8, val 6
    [ 3.686332] acpi backlight index 9, val 7
    [ 3.686356] acpi backlight index 10, val 8
    [ 3.686380] acpi backlight index 11, val 9
    etc.

    Notice that brightness values 0-5 are all mapped to 5. This means that
    if userspace writes any value between 0 and 5 to the brightness sysfs attribute
    and then reads it, it will always return 0, which is somewhat unexpected.

    This is a problem for ie gnome-settings-daemon, which uses read-modify-write
    logic when the users presses the brightness up or down keys. This is done
    this way to take brightness changes from other sources into account.

    On this specific laptop what happens once the brightness has been set to 0,
    is that gsd reads 0, adds 5, writes 5, and on the next brightness up key press
    again reads 0, so things get stuck at the lowest brightness setting.

    Filtering out the duplicate table entries, makes any write to brightness
    read back as the written value as one would expect, fixing this.

    Signed-off-by: Hans de Goede <hdegoede@redhat.com>
    Reviewed-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 | 8 +++++++-
    1 file changed, 7 insertions(+), 1 deletion(-)

    --- a/drivers/acpi/video.c
    +++ b/drivers/acpi/video.c
    @@ -733,6 +733,7 @@ acpi_video_init_brightness(struct acpi_v
    union acpi_object *o;
    struct acpi_video_device_brightness *br = NULL;
    int result = -EINVAL;
    + u32 value;

    if (!ACPI_SUCCESS(acpi_video_device_lcd_query_levels(device, &obj))) {
    ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Could not query available "
    @@ -763,7 +764,12 @@ acpi_video_init_brightness(struct acpi_v
    printk(KERN_ERR PREFIX "Invalid data\n");
    continue;
    }
    - br->levels[count] = (u32) o->integer.value;
    + value = (u32) o->integer.value;
    + /* Skip duplicate entries */
    + if (count > 2 && br->levels[count - 1] == value)
    + continue;
    +
    + br->levels[count] = value;

    if (br->levels[count] > max_level)
    max_level = br->levels[count];



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