path: root/Documentation/kernel-parameters.txt
diff options
authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2015-07-03 01:06:00 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2015-07-03 01:06:00 +0200
commit18d78b64fddc11eb336f01e46ad3303a3f55d039 (patch)
tree806559410131313aa86fa78510e34f1592cbb4ad /Documentation/kernel-parameters.txt
parentce55d01e9b4daee5040777d023d52e6b42d3ad8f (diff)
ACPI / init: Make it possible to override _REV
The platform firmware on some systems expects Linux to return "5" as the supported ACPI revision which makes it expose system configuration information in a special way. For example, based on what ACPI exports as the supported revision, Dell XPS 13 (2015) configures its audio device to either work in HDA mode or in I2S mode, where the former is supposed to be used on Linux until the latter is fully supported (in the kernel as well as in user space). Since ACPI 6 mandates that _REV should return "2" if ACPI 2 or later is supported by the OS, a subsequent change will make that happen, so make it possible to override that on systems where "5" is expected to be returned for Linux to work correctly one them (such as the Dell machine mentioned above). Original-by: Dominik Brodowski <linux@dominikbrodowski.net> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'Documentation/kernel-parameters.txt')
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 61ab1628a057..180102480fc0 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -274,6 +274,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
Format: To spoof as Windows 98: ="Microsoft Windows"
+ acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
+ of 2 which is mandated by ACPI 6) as the supported ACPI
+ specification revision (when using this switch, it may
+ be necessary to carry out a cold reboot _twice_ in a
+ row to make it take effect on the platform firmware).
acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
acpi_osi="string1" # add string1
acpi_osi="!string2" # remove string2

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