PCI: host-common: Add link down handling for Root Ports

The PCIe link, when down, needs to be recovered to bring it back. But on
some platforms, that cannot be done in a generic way as link recovery
procedure is platform specific. Add a new pci_host_handle_link_down() that
could be called by the host bridge drivers for a specific Root Port when
the link goes down.

pci_host_handle_link_down() accepts a 'pci_dev' corresponding to the Root
Port that observed the link down event. If CONFIG_PCIEAER is enabled, it
calls pcie_do_recovery() with 'pci_channel_io_frozen' as the state.  This
will result in the execution of the AER Fatal error handling code.  Since
the link down recovery is pretty much the same as AER Fatal error handling,
reuse pcie_do_recovery() here.

The AER .error_detected() callback will be triggered for all of the
downstream devices, but not for the Root Port itself as there is nothing to
do for the Root Ports in the callbacks. Finally, pci_host_reset_root_port()
will be called for the Root Port, which will reset the Root Port using the
.reset_root_port() callback to recover the link. Once that's done, resume
message will be broadcasted to the bridge and the downstream devices,
indicating successful link recovery.

But if CONFIG_PCIEAER is not enabled in the kernel, only
pci_host_reset_root_port() will be called, which will in turn call
pci_bus_error_reset() to just reset the Root Port as there is no way we
could inform the drivers about link recovery.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Brian Norris <briannorris@chromium.org>
Tested-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Tested-by: Richard Zhu <hongxing.zhu@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260729-pci-port-reset-v9-3-53570b92064d@oss.qualcomm.com

drivers/pci/controller/pci-host-common.c

@@ -13,9 +13,11 @@
 #include <linux/of.h>
 #include <linux/of_address.h>
 #include <linux/of_pci.h>
+#include <linux/pci.h>
 #include <linux/pci-ecam.h>
 #include <linux/platform_device.h>
 
+#include "../pci.h"
 #include "pci-host-common.h"
 
 /**
@@ -342,5 +344,38 @@ bool pci_host_common_d3cold_possible(struct pci_host_bridge *bridge,
 }
 EXPORT_SYMBOL_GPL(pci_host_common_d3cold_possible);
 
+static pci_ers_result_t pci_host_reset_root_port(struct pci_dev *dev)
+{
+	int ret;
+
+	pci_lock_rescan_remove();
+	ret = pci_bus_error_reset(dev);
+	pci_unlock_rescan_remove();
+	if (ret) {
+		pci_err(dev, "Failed to reset Root Port: %d\n", ret);
+		return PCI_ERS_RESULT_DISCONNECT;
+	}
+
+	pci_info(dev, "Root Port has been reset\n");
+
+	return PCI_ERS_RESULT_RECOVERED;
+}
+
+static void pci_host_recover_root_port(struct pci_dev *port)
+{
+#if IS_ENABLED(CONFIG_PCIEAER)
+	pcie_do_recovery(port, pci_channel_io_frozen, pci_host_reset_root_port);
+#else
+	pci_host_reset_root_port(port);
+#endif
+}
+
+void pci_host_handle_link_down(struct pci_dev *port)
+{
+	pci_info(port, "Recovering Root Port due to Link Down\n");
+	pci_host_recover_root_port(port);
+}
+EXPORT_SYMBOL_GPL(pci_host_handle_link_down);
+
 MODULE_DESCRIPTION("Common library for PCI host controller drivers");
 MODULE_LICENSE("GPL v2");

drivers/pci/controller/pci-host-common.h

@@ -48,6 +48,7 @@ int pci_host_common_init(struct platform_device *pdev,
 			 struct pci_host_bridge *bridge,
 			 const struct pci_ecam_ops *ops);
 void pci_host_common_remove(struct platform_device *pdev);
+void pci_host_handle_link_down(struct pci_dev *port);
 
 struct pci_config_window *pci_host_common_ecam_create(struct device *dev,
 	struct pci_host_bridge *bridge, const struct pci_ecam_ops *ops);

drivers/pci/pci.c

@@ -5700,6 +5700,7 @@ int pci_bus_error_reset(struct pci_dev *bridge)
 {
 	return pci_reset_bridge(bridge, PCI_RESET_NO_RESTORE);
 }
+EXPORT_SYMBOL_GPL(pci_bus_error_reset);
 
 int pci_try_reset_bridge(struct pci_dev *bridge)
 {

drivers/pci/pcie/err.c

@@ -292,3 +292,4 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
 
 	return status;
 }
+EXPORT_SYMBOL_GPL(pcie_do_recovery);