On an Asus UX31A (Ivybridge) it is required to load the acpi_video module after the i915kms module to be able to control the brightness (hw.acpi.video.lcd0.brightness) or to successfully resume the machine. Therefore, it is not possible to directly load the acpi_video module at startup (especially because loading the i915kms module from loader.conf leads to a black screen on this machine).
Created attachment 201323 [details] Info of affected system Text file contains the output of pciconf -lv, /var/run/dmesg.boot, freebsd-version, and uname -a in that order. System uses a system and kernel built from source, using the default GENERIC configuration for amd64. Had this issue using the default binary updates as well.
New to bugzilla - didn't realize the attaching of files was its own comment. The system described in the attachment has this same issue, where brightness cannot be controlled if acpi_video is loaded on boot but can be controlled if the module is unloaded and loaded again. The system is a laptop with an Intel Skylake i5 processor and Optimus graphics, using only the Intel card. I have not run into issues with black screens, though that may be because I'm using the i915kms module from the drm-fbsd12.0-kmod package, loaded using kld_list in rc.conf.
I see the same issue -- "where brightness cannot be controlled if acpi_video is loaded on boot but can be controlled if the module is unloaded and loaded again" -- with 14-CURRENT c 20220316 on Framework laptop (Intel i5-1135G7 CPU).
Apparently order matters of values assigned to a variable in /etc/rc.con. Now I have ... kld_list="filemon" kld_list="$kldlist i915kms" kld_list="$kldlist acpi_video" ... ... now the MIBs in /etc/sysctl.conf related to "hw.acpi.video.lcd0" are not reported as unknowns. Earlier I had ... kld_list="filemon" kld_list="$kldlist acpi_video" kld_list="$kldlist i915kms"
That's what I get for not copying-pasta. There were too many technical errors in previous 💩response. I will be grateful if the comment #3 is stricken out|hidden|deleted.🙇♂️ In any case, corrected response ... Apparently order matters of values assigned to a variable in /etc/rc.conf. Now I have ... kld_list="filemon" kld_list="$kld_list i915kms" kld_list="$kld_list acpi_video" ... ... now the brightness related "hw.acpi.video.lcd0" MIBs in /etc/sysctl.conf are not reported as unknowns. Earlier I had ... kld_list="filemon" kld_list="$kld_list acpi_video" kld_list="$kld_list i915kms"
This has been documented about year ago in https://www.freebsd.org/cgi/man.cgi?acpi_video. "compatibility". is this sufficient to close this issue?
Feel free to reopen, but this is by technical design and is documented as such.