linux-kernel - [PATCH] usb: xhci-pci: Fix USB2-only root hub registration

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Message-ID: <20251009142911.6069c164.michal.pecio@gmail.com>
Date: Thu, 9 Oct 2025 14:29:11 +0200
From: Michal Pecio <michal.pecio@...il.com>
To: Arisa Snowbell <arisa.snowbell@...il.com>, Mathias Nyman
 <mathias.nyman@...ux.intel.com>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>
Cc: linux-usb@...r.kernel.org, regressions@...ts.linux.dev, Niklas Neronin
 <niklas.neronin@...ux.intel.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] usb: xhci-pci: Fix USB2-only root hub registration

A recent change to hide USB3 root hubs of USB2-only controllers broke
registration of USB2 root hubs - allow_single_roothub is set too late,
and by this time xhci_run() has already deferred root hub registration
until after the shared HCD is added, which will never happen.

This makes such controllers unusable, but testers didn't notice since
they were only bothered by warnings about empty USB3 root hubs. The bug
caused problems to other people who actually use such HCs and I was
able to confirm it on an ordinary HC by patching to ignore USB3 ports.

Setting allow_single_roothub during early setup fixes things.

Reported-by: Arisa Snowbell <arisa.snowbell@...il.com>
Closes: https://lore.kernel.org/linux-usb/CABpa4MA9unucCoKtSdzJyOLjHNVy+Cwgz5AnAxPkKw6vuox1Nw@mail.gmail.com/
Fixes: 719de070f764 ("usb: xhci-pci: add support for hosts with zero USB3 ports")
Suggested-by: Mathias Nyman <mathias.nyman@...ux.intel.com>
Signed-off-by: Michal Pecio <michal.pecio@...il.com>
---


Arisa, does this version also work?


 drivers/usb/host/xhci-pci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
index 13454bef14d3..cb7f5dd34333 100644
--- a/drivers/usb/host/xhci-pci.c
+++ b/drivers/usb/host/xhci-pci.c
@@ -580,6 +580,7 @@ static int xhci_pci_setup(struct usb_hcd *hcd)
 
 	/* imod_interval is the interrupt moderation value in nanoseconds. */
 	xhci->imod_interval = 40000;
+	xhci->allow_single_roothub = 1;
 
 	retval = xhci_gen_setup(hcd, xhci_pci_quirks);
 	if (retval)
@@ -643,7 +644,6 @@ int xhci_pci_common_probe(struct pci_dev *dev, const struct pci_device_id *id)
 	xhci = hcd_to_xhci(hcd);
 	xhci->reset = reset;
 
-	xhci->allow_single_roothub = 1;
 	if (!xhci_has_one_roothub(xhci)) {
 		xhci->shared_hcd = usb_create_shared_hcd(&xhci_pci_hc_driver, &dev->dev,
 							 pci_name(dev), hcd);
-- 
2.48.1