ACPI: Add facility to disable all _OSI OS vendor strings

This patch introduces "acpi_osi=!" command line to force Linux replying
"UNSUPPORTED" to all of the _OSI strings.  This patch is based on an
ACPICA enhancement - the new API acpi_update_interfaces().

The _OSI object provides the platform with the ability to query OSPM
to determine the set of ACPI related interfaces, behaviors, or
features that the operating system supports.  The argument passed to
the _OSI is a string like the followings:
1. Feature Group String, examples include
   Module Device
   Processor Device
   3.0 _SCP Extensions
   Processor Aggregator Device
   ...
2. OS Vendor String, examples include
   Linux
   FreeBSD
   Windows
   ...

There are AML codes provided in the ACPI namespace written in the
following style to determine OSPM interfaces / features:
    Method(OSCK)
    {
        if (CondRefOf(_OSI, Local0))
        {
            if (\_OSI("Windows"))
            {
                Return (One)
            }
            if (\_OSI("Windows 2006"))
            {
                Return (Ones)
            }
            Return (Zero)
        }
        Return (Zero)
    }

There is a debugging facility implemented in Linux.  Users can pass
"acpi_osi=" boot parameters to the kernel to tune the _OSI evaluation
result so that certain AML codes can be executed.  Current
implementation includes:
1. 'acpi_osi=' - this makes CondRefOf(_OSI, Local0) TRUE
2. 'acpi_osi="Windows"' - this makes \_OSI("Windows") TRUE
3. 'acpi_osi="!Windows"' - this makes \_OSI("Windows") FALSE
The function to implement this feature is also used as a quirk mechanism
in the Linux ACPI subystem.

When _OSI is evaluatated by the AML codes, ACPICA replies "SUPPORTED"
to all Windows operating system vendor strings.  This is because
Windows operating systems return "SUPPORTED" if the argument to the
_OSI method specifies an earlier version of Windows.  Please refer to
the following MSDN document:

How to Identify the Windows Version in ACPI by Using _OSI
http://msdn.microsoft.com/en-us/library/hardware/gg463275.aspx

This adds difficulties when developers want to feed specific Windows
operating system vendor string to the BIOS codes for debugging
purpose, multiple acpi_osi="!xxx" have to be specified in the command
line to force Linux replying "UNSUPPORTED" to the Windows OS vendor
strings listed in the AML codes.

Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Reviewed-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 27 insertions, 2 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 15356aca938..d0d9cf278ae 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -235,10 +235,35 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			Format: To spoof as Windows 98: ="Microsoft Windows"
 
 	acpi_osi=	[HW,ACPI] Modify list of supported OS interface strings
-			acpi_osi="string1"	# add string1 -- only one string
-			acpi_osi="!string2"	# remove built-in string2
+			acpi_osi="string1"	# add string1
+			acpi_osi="!string2"	# remove string2
+			acpi_osi=!		# disable all built-in OS vendor
+						  strings
 			acpi_osi=		# disable all strings
 
+			'acpi_osi=!' can be used in combination with single or
+			multiple 'acpi_osi="string1"' to support specific OS
+			vendor string(s).  Note that such command can only
+			affect the default state of the OS vendor strings, thus
+			it cannot affect the default state of the feature group
+			strings and the current state of the OS vendor strings,
+			specifying it multiple times through kernel command line
+			is meaningless.
+			Examples:
+			  1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
+			     to 'acpi_osi="Windows 2000" acpi_osi=!', they all
+			     can make '_OSI("Windows 2000")' TRUE.
+
+			'acpi_osi=' cannot be used in combination with other
+			'acpi_osi=' command lines, the _OSI method will not
+			exist in the ACPI namespace.  NOTE that such command can
+			only affect the _OSI support state, thus specifying it
+			multiple times through kernel command line is also
+			meaningless.
+			Examples:
+			  1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
+			     FALSE.
+
 	acpi_pm_good	[X86]
 			Override the pmtimer bug detection: force the kernel
 			to assume that this machine's pmtimer latches its value