device/pci_device.c: Scan only one device for PCIe
Only scan one device if it's a PCIe downstream port.
A PCIe downstream port normally leads to a link with only device 0 on
it. As an optimization, scan only for device 0 in that case.
Signed-off-by: Jianjun Wang <jianjun.wang@mediatek.com>
Change-Id: Id184d03b33e1742b18efb3f11aa9b2f81fa03806
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56788
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
diff --git a/src/device/pci_device.c b/src/device/pci_device.c
index 4b5e73b..1075ef7 100644
--- a/src/device/pci_device.c
+++ b/src/device/pci_device.c
@@ -1204,6 +1204,30 @@
}
/**
+ * A PCIe Downstream Port normally leads to a Link with only Device 0 on it
+ * (PCIe spec r5.0, sec 7.3.1). As an optimization, scan only for Device 0 in
+ * that situation.
+ *
+ * @param bus Pointer to the bus structure.
+ */
+static bool pci_bus_only_one_child(struct bus *bus)
+{
+ struct device *bridge = bus->dev;
+ u16 pcie_pos, pcie_flags_reg;
+ int pcie_type;
+
+ pcie_pos = pci_find_capability(bridge, PCI_CAP_ID_PCIE);
+ if (!pcie_pos)
+ return false;
+
+ pcie_flags_reg = pci_read_config16(bridge, pcie_pos + PCI_EXP_FLAGS);
+
+ pcie_type = (pcie_flags_reg & PCI_EXP_FLAGS_TYPE) >> 4;
+
+ return pciexp_is_downstream_port(pcie_type);
+}
+
+/**
* Scan a PCI bus.
*
* Determine the existence of devices and bridges on a PCI bus. If there are
@@ -1232,6 +1256,9 @@
post_code(0x24);
+ if (pci_bus_only_one_child(bus))
+ max_devfn = MIN(max_devfn, 0x07);
+
/*
* Probe all devices/functions on this bus with some optimization for
* non-existence and single function devices.