selectively disable acpi modules

[Ian Smith]

In freebsd-questions Digest, Vol 679, Issue 2, Message: 2
On Mon, 5 Jun 2017 16:04:37 -0400 "Littlefield, Tyler" <tyler at tysdomain.com> wrote:

 > Is there a way to cut out all the acpi modules except the ones you need
 > when building the kernel for FreeBSD 12?

This is rather ambiguous; in the normal meaning of 'modules' there's 
only one, included in kernel by 'device acpi'.  There are other modules 
for various hardware, e.g. here my /boot/loader.conf loads acpi_ibm:

root at x200:~ # kldstat -v | grep acpi
                470 acpi/atdma
                467 acpi/attimer
                465 acpi/atrtc
                438 acpi/fdc
                430 acpi/psmcpnp
                428 acpi/atkbdc
                419 acpi/fpupnp
                418 root/nexus_acpi
                226 acpi/ppc
                25 acpi/acpi_ec
                33 cpu/acpi_perf
                20 nexus/acpi
                32 pci/acpi_pcib
                31 acpi/acpi_pcib
                24 acpi/cpu
                30 acpi/acpi_pci_link
                29 pcib/acpi_pci
                23 acpi/acpi_cmbat
                28 acpi/acpi_lid
                27 acpi/acpi_isab
                22 acpi/acpi_button
                26 acpi/hpet
                38 acpi/acpi_timer
                37 cpu/acpi_throttle
                36 acpi/acpi_tz
                21 acpi/acpi_acad
                35 acpi/acpi_smbat
                283 acpi/uart
                34 acpi/acpi_sysresource
 2    1 0xffffffff8182e000 7fa8     acpi_ibm.ko (/boot/kernel/acpi_ibm.ko)
                 1 acpi/acpi_ibm

acpi(4) lists all ACPI 'sub-drivers' (aka 'sub-devices') and 'features':

 "The acpi driver comprises a set of drivers, which may be selectively
 disabled in case of problems. To disable a sub-driver, list it in the
 kernel environment variable debug.acpi.disabled.  Multiple entries can
 be listed, separated by a space."

https://www.freebsd.org/cgi/man.cgi?query=acpi&manpath=FreeBSD+12-current

It might be clearer if you said just what you wish to disable, and why?

cheers, Ian