FAILED: Patch "Revert "PCI: dwc: Don't wait for link up if driver can detect Link Up event"" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 142d5869f6eec3110adda0ad2d931f5b3c22371d Mon Sep 17 00:00:00 2001
From: Niklas Cassel <[email protected]>
Date: Mon, 22 Dec 2025 07:42:13 +0100
Subject: [PATCH] Revert "PCI: dwc: Don't wait for link up if driver can detect
Link Up event"

This reverts commit 8d3bf19f1b585a3cc0027f508b64c33484db8d0d.

While this fake hotplugging was a nice idea, it has shown that this feature
does not handle PCIe switches correctly:
pci_bus 0004:43: busn_res: can not insert [bus 43-41] under [bus 42-41] (conflicts with (null) [bus 42-41]) pci_bus 0004:43: busn_res: [bus 43-41] end is updated to 43
pci_bus 0004:43: busn_res: can not insert [bus 43] under [bus 42-41] (conflicts with (null) [bus 42-41]) pci 0004:42:00.0: devices behind bridge are unusable because [bus 43] cannot be assigned for them pci_bus 0004:44: busn_res: can not insert [bus 44-41] under [bus 42-41] (conflicts with (null) [bus 42-41]) pci_bus 0004:44: busn_res: [bus 44-41] end is updated to 44
pci_bus 0004:44: busn_res: can not insert [bus 44] under [bus 42-41] (conflicts with (null) [bus 42-41]) pci 0004:42:02.0: devices behind bridge are unusable because [bus 44] cannot be assigned for them pci_bus 0004:45: busn_res: can not insert [bus 45-41] under [bus 42-41] (conflicts with (null) [bus 42-41]) pci_bus 0004:45: busn_res: [bus 45-41] end is updated to 45
pci_bus 0004:45: busn_res: can not insert [bus 45] under [bus 42-41] (conflicts with (null) [bus 42-41]) pci 0004:42:06.0: devices behind bridge are unusable because [bus 45] cannot be assigned for them pci_bus 0004:46: busn_res: can not insert [bus 46-41] under [bus 42-41] (conflicts with (null) [bus 42-41]) pci_bus 0004:46: busn_res: [bus 46-41] end is updated to 46
pci_bus 0004:46: busn_res: can not insert [bus 46] under [bus 42-41] (conflicts with (null) [bus 42-41]) pci 0004:42:0e.0: devices behind bridge are unusable because [bus 46] cannot be assigned for them pci_bus 0004:42: busn_res: [bus 42-41] end is updated to 46
pci_bus 0004:42: busn_res: can not insert [bus 42-46] under [bus 41] (conflicts with (null) [bus 41]) pci 0004:41:00.0: devices behind bridge are unusable because [bus 42-46] cannot be assigned for them pcieport 0004:40:00.0: bridge has subordinate 41 but max busn 46

During the initial scan, PCI core doesn't see the switch and since the Root Port is not hot plug capable, the secondary bus number gets assigned as the subordinate bus number. This means, the PCI core assumes that only one bus will appear behind the Root Port since the Root Port is not hot plug capable.

This works perfectly fine for PCIe endpoints connected to the Root Port, since they don't extend the bus. However, if a PCIe switch is connected, then there is a problem when the downstream busses starts showing up and the PCI core doesn't extend the subordinate bus number and bridge resources after initial scan during boot.

So revert the change that skipped dw_pcie_wait_for_link() if the Link up IRQ was used by a vendor glue driver.

---
 drivers/pci/controller/dwc/pcie-designware-host.c | 10 ++--------
 drivers/pci/controller/dwc/pcie-designware.h      |  1 -
 2 files changed, 2 insertions(+), 9 deletions(-)

index 8c41b90a1db1e..06c02fcc76c89 100644
@@ -665,14 +665,8 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
 			goto err_remove_edma;
 	}
 
-	/*
-	 * Note: Skip the link up delay only when a Link Up IRQ is present.
-	 * If there is no Link Up IRQ, we should not bypass the delay
-	 * because that would require users to manually rescan for devices.
-	 */
-	if (!pp->use_linkup_irq)
-		/* Ignore errors, the link may come up later */
-		dw_pcie_wait_for_link(pci);
+	/* Ignore errors, the link may come up later */
+	dw_pcie_wait_for_link(pci);
 
 	ret = pci_host_probe(bridge);
 	if (ret)

index fc9cf8ce86290..a3a3f6e89a812 100644
@@ -438,7 +438,6 @@ struct dw_pcie_rp {
 	bool			use_atu_msg;
 	int			msg_atu_index;
 	struct resource		*msg_res;
-	bool			use_linkup_irq;
 	struct pci_eq_presets	presets;
 	struct pci_config_window *cfg;
 	bool			ecam_enabled;

2.51.0