[PATCH v2 2/2] PCI: keystone: Add link up check in ks_child_pcie_ops.map_bus()

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From: Kishon Vijay Abraham I <kishon@xxxxxx>

K2G forwards the error triggered by a link-down state (e.g., no connected
endpoint device) on the system bus for PCI configuration transactions;
these errors are reported as an SError at system level, which is fatal and
hangs the system. So fix it similar to how it was done in designware core
driver commit 15b23906347c ("PCI: dwc: Add link up check in

Fixes: 10a797c6e54a ("PCI: dwc: keystone: Use pci_ops for config space accessors")
Signed-off-by: Kishon Vijay Abraham I <kishon@xxxxxx>
Signed-off-by: Siddharth Vadapalli <s-vadapalli@xxxxxx>
 drivers/pci/controller/dwc/pci-keystone.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/pci/controller/dwc/pci-keystone.c b/drivers/pci/controller/dwc/pci-keystone.c
index 3184546ba3b6..ca476fa584e7 100644
--- a/drivers/pci/controller/dwc/pci-keystone.c
+++ b/drivers/pci/controller/dwc/pci-keystone.c
@@ -430,6 +430,17 @@ static void __iomem *ks_pcie_other_map_bus(struct pci_bus *bus,
 	struct keystone_pcie *ks_pcie = to_keystone_pcie(pci);
 	u32 reg;
+	/*
+	 * Checking whether the link is up here is a last line of defense
+	 * against platforms that forward errors on the system bus as
+	 * SError upon PCI configuration transactions issued when the link
+	 * is down. This check is racy by definition and does not stop
+	 * the system from triggering an SError if the link goes down
+	 * after this check is performed.
+	 */
+	if (!dw_pcie_link_up(pci))
+		return NULL;
 	reg = CFG_BUS(bus->number) | CFG_DEVICE(PCI_SLOT(devfn)) |
 	if (!pci_is_root_bus(bus->parent))

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