Linux Might Need To Claim Only ACPI 2.0 Support For BIOS

jones_supa writes Some of us remember the story of why Linux kernel responds "False" when ACPI BIOS asks if the operating system is Linux. We have found yet another case where mimicking the Windows behavior instead of writing to the spec is the right choice if you just want your machine to work properly. The ACPI spec defines the _REV object as evaluating to the revision of the ACPI specification that the OS implements. Linux returns 5 for this, because Linux actually tries to implement ACPI 5.0, but Windows returns 2 (ACPI 2.0), possibly due to legacy reasons. Linux kernel expert Matthew Garrett discovered that still a fair amount of brokenness appears when 5 is returned as the revision, including a Dell machine which left the sound hardware in a misconfigured state. He is proposing a kernel patch which simply reports _REV as 2 on all x86 hardware.

Comments

Add a parameter?

[bill_mcgonigle]

2 might be the right default, but shouldn't we at least allow acpi_version= on the kernel cmdline for people who want to take advantage of the feature spread between 2 and 5?

Not everybody has broken Dell crap, right?

I've been through this myself.

[hey!]

I had a Toshiba laptop where none of the built-in devices like sound or network worked if you booted with ACPI on. It turned out the fix was to fool the bios into thinking it was running Windows by editing the DSDT code. The firmware on this machine actually shut off all the peripherals if it thought it was running some version of Linux.

I've always been mystified as to why Toshiba's engineers did this. And even having that capability in ACPI seems architecturally suspect. I can't see any legitimate reason for the machine's firmware to second guess what to do based on which OS is running on it.