[edk2-platforms][PATCH 1/1] Platform/RaspberryPi/RPi4: Add _DSM ACPI method for 32-bit MMIO xHCI access

["Pete Batard" <pete@akeo.ie>]

With the upcoming release of Windows 11, Microsoft has introduced a new USB
Device-Specific Method (_DSM) function to enforce 64-bit xHCI registers to
be accessed through two sequential 32-bit requests. The new function (Query
controller register access type - Function 6) is documented at:
https://docs.microsoft.com/en-us/windows-hardware/drivers/bringup/usb-device-specific-method---dsm-

Support for this feature is required on the raspberry Pi 4 where there is
a bug/limitation in the xHCI stack that prevents full range 64-bit access
from working correctly. It should be noted that an equivalent for this _DSM
is not required on Linux, as 64-bit xHCI register access is already broken
down into 2x32-bit by the drivers there.

With this _DSM, and unlike what is the case for Windows 10, Windows 11 can
now be installed on the Raspberry Pi 4 without having to alter any of the
installation files, as we were able to validate using the latest Windows 11
Build 22000 Insider image.

Signed-off-by: Pete Batard <pete@akeo.ie>
Tested-by: Pete Batard <pete@akeo.ie>
---
 Platform/RaspberryPi/AcpiTables/Xhci.asl | 21 ++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/Platform/RaspberryPi/AcpiTables/Xhci.asl b/Platform/RaspberryPi/AcpiTables/Xhci.asl
index 9b37277956d9..00b0cd29c69c 100644
--- a/Platform/RaspberryPi/AcpiTables/Xhci.asl
+++ b/Platform/RaspberryPi/AcpiTables/Xhci.asl
@@ -138,6 +138,27 @@ DefinitionBlock (__FILE__, "SSDT", 5, "RPIFDN", "RPI4XHCI", 2)
             Debug = "xHCI enable"
             Store (0x6, CMND)
         }
+
+        /*
+         * Microsoft's USB Device-Specific Methods. See:
+         * https://docs.microsoft.com/en-us/windows-hardware/drivers/bringup/usb-device-specific-method---dsm-
+         */
+        Name (DSMU, ToUUID ("ce2ee385-00e6-48cb-9f05-2edb927c4899"))
+
+        Method (_DSM, 4, Serialized) {
+            If (LEqual (Arg0, DSMU)) {              // USB capabilities UUID
+                Switch (ToInteger (Arg2)) {
+                Case (0) {                          // Function 0: List of supported functions
+                    Return (Buffer () { 0x41 })     // 0x41 - Functions 0 and 6 supported
+                }
+                Case (6) {                          // Function 6: RegisterAccessType
+                    Return (Buffer () { 0x01 })     // 0x01 - Must use 32bit register access
+                }
+                Default { }                         // Unsupported
+                }
+            }
+            return (Buffer () { 0x00 })             // Return 0x00 for anything unsupported
+        }
       } // end XHC0
     } //end SCB0
   } //end scope sb
-- 
2.30.2.windows.1