OK, then you're hitting multiple issues, as it seems. The inconsistent value read from sysfs was addressed by my patch. But, I suppose that the main reason of the non-functional backlight is that the driver misdetected the backlight control over aux. I refreshed again the KMP with a hack patch to disable the aux support. Please give it a try later again. This will show a line "XXX ext_caps=0x..." in kernel log.