PCI: Check for PCIe Link downtraining

When both ends of a PCIe Link are capable of a higher bandwidth than is
currently in use, the Link is said to be "downtrained".  A downtrained Link
may indicate hardware or configuration problems in the system, but it's
hard to identify such Links from userspace.

Refactor pcie_print_link_status() so it continues to always print PCIe
bandwidth information, as several NIC drivers desire.

Add a new internal __pcie_print_link_status() to emit a message only when a
device's bandwidth is constrained by the fabric and call it from the PCI
core for all devices, which identifies all downtrained Links.  It also
emits messages for a few cases that are technically not downtrained, such
as a x4 device in an open-ended x1 slot.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
[bhelgaas: changelog, move __pcie_print_link_status() declaration to
drivers/pci/, rename pcie_check_upstream_link() to
pcie_report_downtraining()]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 7c0c8ab94bcf..71412db3cbeb 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2223,6 +2223,25 @@ static struct pci_dev *pci_scan_device(struct pci_bus *bus, int devfn)
 	return dev;
 }
 
+static void pcie_report_downtraining(struct pci_dev *dev)
+{
+	if (!pci_is_pcie(dev))
+		return;
+
+	/* Look from the device up to avoid downstream ports with no devices */
+	if ((pci_pcie_type(dev) != PCI_EXP_TYPE_ENDPOINT) &&
+	    (pci_pcie_type(dev) != PCI_EXP_TYPE_LEG_END) &&
+	    (pci_pcie_type(dev) != PCI_EXP_TYPE_UPSTREAM))
+		return;
+
+	/* Multi-function PCIe devices share the same link/status */
+	if (PCI_FUNC(dev->devfn) != 0 || dev->is_virtfn)
+		return;
+
+	/* Print link status only if the device is constrained by the fabric */
+	__pcie_print_link_status(dev, false);
+}
+
 static void pci_init_capabilities(struct pci_dev *dev)
 {
 	/* Enhanced Allocation */
@@ -2258,6 +2277,8 @@ static void pci_init_capabilities(struct pci_dev *dev)
 	/* Advanced Error Reporting */
 	pci_aer_init(dev);
 
+	pcie_report_downtraining(dev);
+
 	if (pci_probe_reset_function(dev) == 0)
 		dev->reset_fn = 1;
 }