I found another solution, seems to be better because, kernel version 4.4.0.21 has a bug within the suspend mode(sometimes works and sometimes not) at least, happened to me in a Dell latitude e6420 and also this bug of the backlight, so to fix it I updated the kernel version to 4.7.5 -- The only problem was that wireless stopped working, so to fix it I connected through wired connection and I changed the driver, after that all works well!
I found another solution, seems to be better because, kernel version 4.4.0.21 has a bug within the suspend mode(sometimes works and sometimes not) at least, happened to me in a Dell latitude e6420 and also this bug of the backlight, so to fix it I updated the kernel version to 4.7.5 -- The only problem was that wireless stopped working, so to fix it I connected through wired connection and I changed the driver, after that all works well!
check this: http:// askubuntu. com/questions/ 574920/ upgrading- to-3-18- kernel- causes- wireless- not-to- work
**may be help:)
Sorry for my bad english.