Comment 51 for bug 847001

Same issue here with Ubuntu 18.04 on Dell Inspiron 15R 5521.

I have tried changing
       GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
       GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor".
on /etc/default/grub and did not help.

Also tried the solution on and did not do anything.
Both brightness and volume keys are really slow do adjust and the brightness ones always freeze the screen for good 5 seconds.