Persimmon DSDT: Add OSC method

The _OSC method is used to tell the OS what capabilities
it can take control over from the firmware.  This method
is described in chapter 6.2.9 of the ACPI spec v3.0.
The method takes 4 inputs (UUID, Rev ID, Input Count,
and Capabilities Buffer) and returns a Capabilites
Buffer the same size as the input Buffer.  This Buffer
is generally 3 Dwords long consisting of an Errors
Dword, a Supported Capabilities Dword, and a Control
Dword.  The OS will request control of certain
capabilities and the firmware must grant or deny control
of those features.  We do not want to have control over
anything so let the OS control as much as it can.

The _OSC method is required for PCIe devices and dmesg
checks for its existence and issues an error if it is
not found.

Change-Id: I1494285def7440972f0549b7cb73eb94dafc72c2
Signed-off-by: Mike Loptien <mike.loptien@se-eng.com>
Reviewed-on: http://review.coreboot.org/2684
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/mainboard/amd/persimmon/dsdt.asl

@@ -1157,8 +1157,20 @@ DefinitionBlock (
 		Device(PCI0) {
 			External (TOM1)
 			External (TOM2)
-			Name(_HID, EISAID("PNP0A03"))
+			Name(_HID, EISAID("PNP0A08"))	/* PCI Express Root Bridge */
+			Name(_CID, EISAID("PNP0A03"))	/* PCI Root Bridge */
 			Name(_ADR, 0x00180000)	/* Dev# = BSP Dev#, Func# = 0 */
+
+			/* Operating System Capabilities Method */
+			Method(_OSC,4)
+			{	/* Check for proper PCI/PCIe UUID */
+				If(LEqual(Arg0,ToUUID("33DB4D5B-1FF7-401C-9657-7441C03DD766")))
+				{
+					/* Let OS control everything */
+					Return (Arg3)
+				}
+			}
+
 			Method(_BBN, 0) { /* Bus number = 0 */
 				Return(0)
 			}