linuxkpi: Add backlight support

[manu]

Summary

Add backlight function to linuxkpi.
Graphics drivers expose the backlight of the panel directly so allow them to use the backlight subsystem so
user can use backlight(8) to configure them.

Sponsored-by: The FreeBSD Foundation.

Test Plan

Tested using https://github.com/freebsd/drm-kmod/tree/backlight on intel and amd laptop.

[manu]

Remove changes that should have been part of D26250

[zeising]

Nice work!
How is the backlight adjustments exposed to users?
Do we need to change drm-current-kmod?

sys/compat/linuxkpi/common/include/linux/backlight.h

32–33

Should this be _LINUX_BACKLIGHT_H_ ?

93

I think you should add something like
/* !_LINUX_BACKLIGHT_H */ here

[manu]

In D26253#583404, @zeising wrote:

Nice work!
How is the backlight adjustments exposed to users?

See https://reviews.freebsd.org/D26251

Do we need to change drm-current-kmod?

Yes I think so, I'll not commit before making a PR (if required).

sys/compat/linuxkpi/common/include/linux/backlight.h

32–33

Yeah, I'll update

93

It's not needed but indeed better.

[• hselasky]

sys/compat/linuxkpi/common/include/linux/backlight.h

77

Please use function macros here !

[manu]

Address @hselasky's comments.

[• hselasky]

sys/modules/linuxkpi/Makefile

26

I think backlight_if.h should be added to LINUXKPI_GENSRCS definition in

sys/conf/kmod.mk:LINUXKPI_GENSRCS

[• hselasky]

sys/modules/linuxkpi/Makefile

26

Forget that. It is only used when building the LinuxKPI!

[manu]

Add backlight_if.h to LINUXKPI_GENSRC variable.

[manu]

No this is the right place for _if.h files.

[manu]

Add support for GETINFO and free backlight data.

[• hselasky]

Don't forget to bump the FreeBSD KERNEL version after this.

[manu]

Commited in r366372