Clarifications on ACPI driver

Michael Powell nightrecon at hotmail.com
Wed Feb 4 20:50:33 UTC 2015


Andrea Venturoli wrote:

> Hello.
> 
> I read in the handbook (12.13.1) "the acpi(4) driver is loaded by
> default at system boot and should *not* be compiled into the kernel".
> 
> Yet I see "device acpi" in GENERIC.

This is only so for the 32-bit i386 build. You will not see this in the 64-
bit x86_64 build.

> Aren't those two things in contrast?

My perception here is the confusion may arise from the 64-bit vs 32-bit 
systems; the above is applicable to the 64-bit build while a 32-bit build 
still uses the deprecated 'device acpi'. 
 
> Is the information in the handbook outdated? Wrong?
> Does it mean something different to what I believe it means?
> 

This could probably be improved in the Handbook by including the 32 vs 64 
bit differences as outlined above. 
 
> 
> What is "options         ACPI_DMAR"? What does it do?

This I have no idea.
 
> Is it ok to add "device acpi_video" to a kernel config?

I don't know enough about ACPI in FreeBSD in general, but historically many 
acpi situations have been moreso a problem wrt to laptops. There are a few 
acpi modules that cover some specific laptop hardwares, but this is still 
not totally comprehensive. Some piece of the problem has been that 
manufacturers don't release the information the devs need.  
 
A quick perusal of man acpi_video looks like it may be useful in certain 
situations, most seemingly wrt to laptop display choosing and/or screen 
brightness. Since I do not run FreeBSD on a laptop I just don't know enough 
about this. In short, for a 32-bit system you could give it a try, but 
should you try to place 'device acpi' into a 64-bit build it will bomb.

-Mike




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