Documentation/acpi: add Windows-specific documentation

When using the Windows fast startup mechanism which is enabled by default, Windows will use a cached version of the ACPI tables during normal boots after a clean shutdown. Since I've run into this issue and spent quite a bit of time debugging the wrong issue due to this, better document this possibly unexpected behavior. Signed-off-by: Felix Held <[email protected]> Change-Id: Ia9e65f6a3aff13fa54abe68c8f5fcbf9bc6efc1a Reviewed-on: https://review.coreboot.org/c/coreboot/+/77354 Tested-by: build bot (Jenkins) <[email protected]> Reviewed-by: Nico Huber <[email protected]> Reviewed-by: Paul Menzel <[email protected]> Reviewed-by: Matt DeVillier <[email protected]>
hwpplayers · Aug 22, 2023 · 048c2f2 · 048c2f2
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diff --git a/Documentation/acpi/index.md b/Documentation/acpi/index.md
@@ -11,6 +11,9 @@ upwards.
 
 - [GPIO toggling in ACPI AML](gpio.md)
 
+## Windows-specific ACPI documentation
+
+- [Windows-specific documentation](windows.md)
 
 ##  ACPI specification - Useful links
 

diff --git a/Documentation/acpi/windows.md b/Documentation/acpi/windows.md
@@ -0,0 +1,9 @@
+# Testing ACPI changes under Windows
+
+When testing ACPI changes in coreboot against Windows 8 or newer, beware that
+during a normal boot after a clean shutdown, Windows will use the fast startup
+mechanism which results in it not evaluating the changed ACPI code but instead
+using some cached version which won't include the changes that were supposed to
+be tested. In order for Windows to actually use the new ACPI tables, either
+disable the fast startup or just tell Windows to do a reboot which will make it
+read and use the ACPI tables in memory instead of an outdated cached version.