On 01/06/2010 02:22 PM, Len Brown wrote:
using _OSI is not "a similar method to Windows".
The BIOS does not need to invoke _OSI to determine if
it should expose a properly functioning ACPI reset or not.
Windows XP simply demanded it, and the box failed WHQL
if it did not work.
http://download.microsoft.com/download/7/E/7/7E7662CF-CBEA-470B-A97E-CE7CE0D98DC2/WinACPI_OSI.docx
was what I was referring to:
"By using the _OSI method, ASL writers can easily determine the version
of the ACPI interfaces that the host operating system supports. This
versioning method provides a solution for creating firmware that can
support future operating systems and enable the operating system to
change behavior based on the requested interface levels."
We know that this is used for deciding whether or not to block system IO
accesses, but it wouldn't surprise me if it's also used to determine
other functionality like whether or not the ACPI interface is used for
rebooting.
I've looked at _OSI use in over a hundred DSDTs and never
seen run-time re-configuration of reset support.
I do not think the BIOS has a run-time decision to make here.
If a box is designed to support Windows XP and newer, it is
likely that ACPI_RESET is simply valid and XP blindly uses it.
If reset fails, the box doesn't pass WHQL and the box is fixed.
If W2K is run on that box, ACPI_RESET is still valid, just that
W2K chooses to not write to it.
Further, there is no _guarantee_ that a BIOS will invoke _OSI
at all, let alone a _rule_ for what _OSI() strings the BIOS
will choose to query to trigger its Windows specific
compatibility hooks -- even if common practice is for
a desktop BIOS to evaluate _OSI strings in sequence
up throught he most recent version of Windows it
knows about...
It's effectively guaranteed if the system is validated with Windows.
today's common industry practice != future guarantee
We can't rely on blind use of _OSI to mean "new enough", since
it was supported back in W2K era. That means we have to parse
the OSI strings. But what happens when a BIOS writer decides to
evaluate _OSI("Windows Future") without evaluating any of the
old strings we know about? We would disable ACPI reset on such
a future box?
Well, the use of such OSI calls to indicate the BIOS supports
OS-specific features is explicitly recommended by Microsoft, i.e. see
the document linked at
http://www.microsoft.com/whdc/system/pnppwr/powermgmt/WinACPI_OSI.mspx :
"Place the routine that identifies the operating system in an _INI
method under the \_SB scope so that _OSI can run as early as possible.
This placement is important because the operating system makes features
available based on the string argument to the _OSI method."
Also from http://www.microsoft.com/taiwan/whdc/archive/BIOSAML.mspx :
"By passing the string "Windows 2001" into the _OSI method, the BIOS
indicates to the operating system that the BIOS is aware of and
compatible with the ACPI implementation and feature set of Windows XP."
They don't explicitly say how to do it, but the implication is that one
should use the sort of method I've seen in various BIOSes, where it
starts with checking _OSI on the newest Windows version and tries all
known older Windows versions, and stops when it finds the first one that
succeeds..
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