dm/pci: Change the first CFG read to Vendor ID in enumeration

As the PCIe specification recommend reading the Vendor ID register
to determine if a Function is present, read the Vendor ID of a
non-existent Function must not result in system error, so we'd better
make the first CFG read to Vendor ID instead of Header Type register
in the PCIe enumeration.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

diff --git a/drivers/pci/pci-uclass.c b/drivers/pci/pci-uclass.c
index 0c52337..2cf55cb 100644 (file)
--- a/drivers/pci/pci-uclass.c
+++ b/drivers/pci/pci-uclass.c
@@ -774,16 +774,19 @@ int pci_bind_bus_devices(struct udevice *bus)
                        found_multi = false;
                if (PCI_FUNC(bdf) && !found_multi)
                        continue;
+
                /* Check only the first access, we don't expect problems */
-               ret = pci_bus_read_config(bus, bdf, PCI_HEADER_TYPE,
-                                         &header_type, PCI_SIZE_8);
+               ret = pci_bus_read_config(bus, bdf, PCI_VENDOR_ID, &vendor,
+                                         PCI_SIZE_16);
                if (ret)
                        goto error;
-               pci_bus_read_config(bus, bdf, PCI_VENDOR_ID, &vendor,
-                                   PCI_SIZE_16);
+
                if (vendor == 0xffff || vendor == 0x0000)
                        continue;
 
+               pci_bus_read_config(bus, bdf, PCI_HEADER_TYPE,
+                                   &header_type, PCI_SIZE_8);
+
                if (!PCI_FUNC(bdf))
                        found_multi = header_type & 0x80;