Hello,

Has anyone else that has installed Ubuntu 15.04 fresh on the XPS 13 9343 noticed that the granularity of the brightness control is worse than compared to the stock Ubuntu provided by Dell? What I'm finding is that for any value on the slider from about 20%-100% there's very l little difference in brightness; it's slight differences in "very bright". Below 20% it rapidly jumps to completely off.

I've found some posts that suggest that it's down to the Linux kernel switching from a logarithmic scale to a linear one:

• https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1341108
• https://marc.info/?l=linux-acpi&m=140600387808371&w=2

Right now I'm running 3.19.0-22-generic, the most up to date kernel with Ubuntu 15.04. I've tried to use kernel parameters suggested such as acpi_backlight=vendor or acpi_backlight=0 but these seem to only disable the brightness controls completely.

Can anyone else confirm this experience and if so has anyone got a fix? If not, next steps for me will be to try earlier kernels to prove the regression (since I could have imagined it) and then try later ones to see if it's already been addressed for future releases.

Regards,
Bob