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The Xiaomi Mi Pad 2 tablet uses an ACPI enumerated LP8556 backlight controller for its LCD-panel, with a Xiaomi specific ACPI HID of "XMCC0001", add support for this. Note the new "if (id)" check also fixes a NULL pointer deref when a user tries to manually bind the driver from sysfs. When CONFIG_ACPI is disabled acpi_match_device() will always return NULL, so the lp855x_parse_acpi() call will get optimized away. Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org> Signed-off-by: Hans de Goede <hdegoede@redhat.com> Signed-off-by: Lee Jones <lee.jones@linaro.org> Link: https://lore.kernel.org/r/20211102225504.18920-3-hdegoede@redhat.com