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-rw-r--r--Documentation/acpi/index.md2
-rw-r--r--Documentation/acpi/uid.md14
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diff --git a/Documentation/acpi/index.md b/Documentation/acpi/index.md
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--- a/Documentation/acpi/index.md
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@@ -2,6 +2,8 @@
This section contains documentation about coreboot on ACPI.
+- [SSDT UID generation](uid.md)
+
## GPIO
- [GPIO toggling in ACPI AML](gpio.md)
diff --git a/Documentation/acpi/uid.md b/Documentation/acpi/uid.md
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+# ACPI SSDT \_UID generation
+
+According to the ACPI spec:
+
+> The _UID must be unique across all devices with either a common _HID or _CID.
+
+
+When generating SSDTs in coreboot the independent drivers don't know
+which \_UID is already in use for a specific \_HID or \_CID. To generate
+unique \_UIDs the ACPI device's path is hashed and used as ID. As every ACPI
+device has a different path, the hash will be also different for every device.
+
+Windows 10 verifies all devices with the same \_HID or \_CID and makes
+sure that no \_UID is duplicated. If it is it'll BSOD.