Dell initially place all his BIOS on a repository to be used by dellBiosUpdate tool but now it is not longer updated.
To get the latest BIOS for your pc you have to download the Windows BIOS package and extract the HDR data using wine (example for Latitude E6500):
wine E6500A19.EXE -writehdrfile
A new file will be created: E6500A19.hdr
Now we can update the BIOS as usual:
sudo apt-get install smbios-utils
sudo modprobe dell_rbu
sudo dellBiosUpdate -u -f ./E6500A19.hdr
Restart your Linux box and enjoy!
Thanks, you saved my day