PCI: Add pci_bus_crs_vendor_id() to detect CRS response data

Add pci_bus_crs_vendor_id() to determine whether data returned for a config
read of the Vendor ID indicates a Configuration Request Retry Status (CRS)
response.

Per PCIe r3.1, sec 2.3.2, this data is only returned if:

  - CRS Software Visibility is enabled,
  - a config read includes both bytes of the Vendor ID, and
  - the read receives a CRS completion
Signed-off-by: NSinan Kaya <okaya@codeaurora.org>
[bhelgaas: changelog, change name to pci_bus_crs_vendor_id(), make static
in probe.c, use it in pci_bus_read_dev_vendor_id()]
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

drivers/pci/probe.c

@@ -1853,6 +1853,11 @@ struct pci_dev *pci_alloc_dev(struct pci_bus *bus)
 }
 EXPORT_SYMBOL(pci_alloc_dev);
 
+static bool pci_bus_crs_vendor_id(u32 l)
+{
+	return (l & 0xffff) == 0x0001;
+}
+
 bool pci_bus_read_dev_vendor_id(struct pci_bus *bus, int devfn, u32 *l,
 				int crs_timeout)
 {
@@ -1872,7 +1877,7 @@ bool pci_bus_read_dev_vendor_id(struct pci_bus *bus, int devfn, u32 *l,
 	 * by the PCIe spec.  Ignore the device ID and only check for
 	 * (vendor id == 1).
 	 */
-	while ((*l & 0xffff) == 0x0001) {
+	while (pci_bus_crs_vendor_id(*l)) {
 		if (!crs_timeout)
 			return false;