PCI/EDR: Align EDR_PORT_LOCATE_DSM with PCI Firmware r3.3

The "Downstream Port Containment related Enhancements" ECN of Jan 28, 2019
(document 12888 below), defined the EDR_PORT_LOCATE_DSM function with
Revision ID 5 with a return value encoding (Bits 2:0 = Function, Bits 7:3 =
Device, Bits 15:8 = Bus).  When the ECN was integrated into PCI Firmware
r3.3, sec 4.6.13, Bit 31 was added to indicate success or failure.

Check Bit 31 for failure in acpi_dpc_port_get().

Link: https://lore.kernel.org/r/20240501022543.1626025-1-sathyanarayanan.kuppuswamy@linux.intel.com
Link: https://members.pcisig.com/wg/PCI-SIG/document/12888
Fixes: ac1c8e3 ("PCI/DPC: Add Error Disconnect Recover (EDR) support")
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
[bhelgaas: split into two patches, update commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Satish Thatchanamurthy <Satish.Thatchanamurt@Dell.com> # one platform

Author: Kuppuswamy Sathyanarayanan

drivers/pci/pcie/edr.c

@@ -80,8 +80,9 @@ static struct pci_dev *acpi_dpc_port_get(struct pci_dev *pdev)
 	u16 port;
 
 	/*
-	 * Behavior when calling unsupported _DSM functions is undefined,
-	 * so check whether EDR_PORT_DPC_ENABLE_DSM is supported.
+	 * If EDR_PORT_LOCATE_DSM is not implemented under the target of
+	 * EDR, the target is the port that experienced the containment
+	 * event (PCI Firmware r3.3, sec 4.6.13).
 	 */
 	if (!acpi_check_dsm(adev->handle, &pci_acpi_dsm_guid, 5,
 			    1ULL << EDR_PORT_LOCATE_DSM))
@@ -98,6 +99,16 @@ static struct pci_dev *acpi_dpc_port_get(struct pci_dev *pdev)
 		return NULL;
 	}
 
+	/*
+	 * Bit 31 represents the success/failure of the operation. If bit
+	 * 31 is set, the operation failed.
+	 */
+	if (obj->integer.value & BIT(31)) {
+		ACPI_FREE(obj);
+		pci_err(pdev, "Locate Port _DSM failed\n");
+		return NULL;
+	}
+
 	/*
 	 * Firmware returns DPC port BDF details in following format:
 	 *	15:8 = bus