Should we xref acpi_video as well, since it can be used for the same thing (amongts other things). You should probably add the xref in acpi_video to this tool as well.

I don't think so, for me acpi_video is useless.
It doesn't work on all (minus one not tested) my laptops without loading the drm driver and sometimes doesn't even work after.

Since a lot of people and guides mention acpi_video, and specifically the brightness sysctl, I thought it was a good idea, to draw attention to this tool.

I plan to send a mail to current/x11 after commiting all this, I think this will draw more attention than in a man page that people won't read if they know about the sysctl :)

ok :)

I guess this patch needs to change the man8 makefile? This man9 thing was already in D26250