firmware-guide/acpi/osi.rst

16 This document explains how and why the BIOS and Linux should use these methods.
22 Linux runs on two groups of machines -- those that are tested by the OEM
23 to be compatible with Linux, and those that were never tested with Linux,
24 but where Linux was installed to replace the original OS (Windows or OSX).
31 exposes Linux to an entire category of BIOS bugs.
32 For this reason, Linux _OSI defaults must continue to claim compatibility
35 But Linux isn't actually compatible with Windows, and the Linux community
36 has also been hurt with regressions when Linux adds the latest version of
41 What should an OEM do if they want to support Linux and Windows
43 for Linux to deal with how Linux is different from Windows.
46 Linux kernel and changes to Linux kernel drivers to execute this custom
48 method (_DSM) that is called from the Linux kernel.
51 _OSI("Linux-OEM-my_interface_name")
60 any custom Linux-* strings by default.
94 Linux answers "Microsoft Windows NT" to please that BIOS idiom.
120 Linux had no choice but to also return TRUE to _OSI("Windows 2001")
124 This strategy is problematic, as Linux is never completely compatible with
128 Not to be out-done, the Linux community made things worse by returning TRUE
129 to _OSI("Linux").  Doing so is even worse than the Windows misuse
130 of _OSI, as "Linux" does not even contain any version information.
131 _OSI("Linux") led to some BIOS' malfunctioning due to BIOS writer's
132 using it in untested BIOS flows.  But some OEM's used _OSI("Linux")
133 in tested flows to support real Linux features.  In 2009, Linux
134 removed _OSI("Linux"), and added a cmdline parameter to restore it
138 No BIOS should use _OSI("Linux").
140 The result is a strategy for Linux to maximize compatibility with
149 Since _OSI("Linux") went away, some BIOS writers used _REV
150 to support Linux and Windows differences in the same BIOS.
155 Modern Windows returns _REV = 2.  Linux used ACPI_CA_SUPPORT_LEVEL,
159 for _REV = 3, and do something for Linux, but when Linux returned
162 In response to this problem, Linux returns _REV = 2 always,
172 Like Linux's _OSI("*Windows*") strategy, Linux defaults to
177 Starting in Linux-3.18, the kernel answered YES to _OSI("Darwin")
183 The Linux-3.18 change in default caused power regressions on Mac
185 the default via cmdline "acpi_osi=!Darwin".  Linux-4.7 fixed
187 we hope to see Mac Thunderbolt power management support in Linux-4.11.