linux-kernel - Re: XHCI without USB2 ports

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Message-ID: <1b2558f7-94ea-123e-dd3f-b43ecd85c2ef@linux.intel.com>
Date: Tue, 13 Feb 2024 11:59:51 +0200
From: Mathias Nyman <mathias.nyman@...ux.intel.com>
To: Jan Henrik Weinstock <jan@....re>, mathias.nyman@...el.com,
 gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Lukas Jünger <lukas@....re>
Subject: Re: XHCI without USB2 ports

On 12.2.2024 20.39, Jan Henrik Weinstock wrote:
> Hi all,
> 
> I am currently working on an XHCI platform device simulation model. I
> noticed that the Linux driver (Linux 6.5.6 xhci-hcd) stops working
> when I configure the model without any USB2 ports. During an interrupt
> (TRB_PORT_STATUS), I only get "xhci-hcd 12100000.usb: ignore port
> event for removed USB3 hcd."
> 
> During xhci_irq, in handle_port_status, xhci->shared_hcd is NULL [1],
> so the interrupt gets ignored. However, shared_hcd would only ever be
> allocated during xhci_plat_probe [2], if the device has both USB2 and
> USB3 ports, i.e. xhci_has_one_roothub returns false [3].
> 
> Without any USB2 ports, a shared_hcd will never be allocated in the
> first place, and handle_port_status will always exit early.

This is true.
That port handling code is from a time before xhci driver supported single
roothub setups.

I think all single roothub cases so far have been xHC hosts with only USB2
ports. This is probably the first one with only USB3 ports.

I have a vague memory that USB3 specification would require USB3 ports to
be backwards compatible, and support USB2.

But xhci driver could still support it, does this change help:

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index f0d8a607ff21..6ef081f5ef05 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1893,7 +1893,8 @@ static void handle_port_status(struct xhci_hcd *xhci,
         }
  
         /* We might get interrupts after shared_hcd is removed */
-       if (port->rhub == &xhci->usb3_rhub && xhci->shared_hcd == NULL) {
+       if (!xhci_has_one_roothub(xhci) && xhci->shared_hcd == NULL &&
+           port->rhub == &xhci->usb3_rhub) {
                 xhci_dbg(xhci, "ignore port event for removed USB3 hcd\n");
                 bogus_port_status = true;
                 goto cleanup;

Thanks
Mathias