Re: [PATCH 1/1] PCI/bwctrl: Disable BW controller on Intel P45 using a quirk

[Roland Ziegler]

On Fri, 16 Mar 2026 13:15:13 +0100, Ilpo Jarvinen wrote:
> The commit 665745f27487 ("PCI/bwctrl: Re-add BW notification portdrv as
> PCIe BW controller") was found to lead to a boot hang on a Intel P45
> system. Testing without setting Link Bandwidth Management Interrupt
> Enable (LBMIE) and Link Autonomous Bandwidth Interrupt Enable (LABIE)
> in bwctrl allowed system to come up.
>
> Add no_bw_notif into the struct pci_dev and quirk Intel P45 Root Port
> with it.

The commit 665745f27487 re-added BW notification support in bwctrl,
but on Intel P45 root ports it can cause a boot hang when both LBMIE
and LABIE are enabled.

This patch modifies bwctrl to allow the interrupts safely. For ports
marked no_bw_notif, each interrupt is enabled separately, preventing
the hang while keeping BW notifications functional.

Patch has been tested since kernel v6.13 on P45 hardware without issues.

---

Patch:

--- a/drivers/pci/pcie/bwctrl.c
+++ b/drivers/pci/pcie/bwctrl.c
@@ -190,8 +190,13 @@
 	if (ret == PCIBIOS_SUCCESSFUL && link_status & PCI_EXP_LNKSTA_LBMS)
 		set_bit(PCI_LINK_LBMS_SEEN, &port->priv_flags);
 
-	pcie_capability_set_word(port, PCI_EXP_LNKCTL,
-				 PCI_EXP_LNKCTL_LBMIE | PCI_EXP_LNKCTL_LABIE);
+	if (port->no_bw_notif) {
+		pcie_capability_set_word(port, PCI_EXP_LNKCTL, PCI_EXP_LNKCTL_LBMIE);
+		pcie_capability_set_word(port, PCI_EXP_LNKCTL, PCI_EXP_LNKCTL_LABIE);
+	} else
+		pcie_capability_set_word(port, PCI_EXP_LNKCTL,
+					 PCI_EXP_LNKCTL_LBMIE | PCI_EXP_LNKCTL_LABIE);
+
 	pcie_capability_write_word(port, PCI_EXP_LNKSTA,
 				   PCI_EXP_LNKSTA_LBMS | PCI_EXP_LNKSTA_LABS);
 
@@ -250,9 +255,6 @@
 	struct pci_dev *port = srv->port;
 	int ret;
 
-	if (port->no_bw_notif)
-		return -ENODEV;
-
 	/* Can happen if we run out of bus numbers during enumeration. */
 	if (!port->subordinate)
 		return -ENODEV;

Fixes: 665745f27487 ("PCI/bwctrl: Re-add BW notification portdrv as PCIe BW controller")
Link: https://lore.kernel.org/lkml/20260116131513.2359-1-ilpo.jarvinen@xxxxxxxxxxxxxxx/

Signed-off-by: Roland <ea3393@xxxxxxxxxx>