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

[Kishon Vijay Abraham I <kishon@ti.com>]

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
dw_child_pcie_ops.map_bus()").

Fixes: 10a797c6e54a ("PCI: dwc: keystone: Use pci_ops for config space accessors")
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Cc: <stable@vger.kernel.org> # v5.10
---
 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 7171ea70da49..4de8c8e5e3f2 100644
--- a/drivers/pci/controller/dwc/pci-keystone.c
+++ b/drivers/pci/controller/dwc/pci-keystone.c
@@ -432,6 +432,17 @@ 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)) |
 		CFG_FUNC(PCI_FUNC(devfn));
 	if (!pci_is_root_bus(bus->parent))
-- 
2.17.1