cxl/acpi: Do not add DSDT disabled ACPI0016 host bridge ports

commit a7bfaad upstream.

During CXL ACPI probe, host bridge ports are discovered by scanning
the ACPI0017 root port for ACPI0016 host bridge devices. The scan
matches on the hardware id of "ACPI0016". An issue occurs when an
ACPI0016 device is defined in the DSDT yet disabled on the platform.
Attempts by the cxl_acpi driver to add host bridge ports using a
disabled device fails, and the entire cxl_acpi probe fails.

The DSDT table includes an _STA method that sets the status and the
ACPI subsystem has checks available to examine it. One such check is
in the acpi_pci_find_root() path. Move the call to acpi_pci_find_root()
to the matching function to prevent this issue when adding either
upstream or downstream ports.

Suggested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Alison Schofield <alison.schofield@intel.com>
Fixes: 7d4b5ca ("cxl/acpi: Add downstream port data to cxl_port instances")
Cc: <stable@vger.kernel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/163072203957.2250120.2178685721061002124.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/cxl/acpi.c

@@ -243,6 +243,9 @@ static struct acpi_device *to_cxl_host_bridge(struct device *dev)
 {
 	struct acpi_device *adev = to_acpi_device(dev);
 
+	if (!acpi_pci_find_root(adev->handle))
+		return NULL;
+
 	if (strcmp(acpi_device_hid(adev), "ACPI0016") == 0)
 		return adev;
 	return NULL;
@@ -266,10 +269,6 @@ static int add_host_bridge_uport(struct device *match, void *arg)
 	if (!bridge)
 		return 0;
 
-	pci_root = acpi_pci_find_root(bridge->handle);
-	if (!pci_root)
-		return -ENXIO;
-
 	dport = find_dport_by_dev(root_port, match);
 	if (!dport) {
 		dev_dbg(host, "host bridge expected and not found\n");
@@ -282,6 +281,11 @@ static int add_host_bridge_uport(struct device *match, void *arg)
 		return PTR_ERR(port);
 	dev_dbg(host, "%s: add: %s\n", dev_name(match), dev_name(&port->dev));
 
+	/*
+	 * Note that this lookup already succeeded in
+	 * to_cxl_host_bridge(), so no need to check for failure here
+	 */
+	pci_root = acpi_pci_find_root(bridge->handle);
 	ctx = (struct cxl_walk_context){
 		.dev = host,
 		.root = pci_root->bus,