While upgrading your Debian Stretch, you can come up with this message :
W: Possible missing firmware /lib/firmware/i915/kbl_huc_ver02_00_1810.bin for module i915
W: Possible missing firmware /lib/firmware/i915/bxt_huc_ver01_07_1398.bin for module i915
W: Possible missing firmware /lib/firmware/i915/skl_huc_ver01_07_1398.bin for module i915
This has been referenced as a bug :
If you can’t upgrade to Debian Buster, there is a possible workaround
Otherwise, after switching to Buster, the available version of firmware-misc-nonfree provides the missing firmwares.