Re: [PATCH 23/23] usb: xhci: Add debugfs support for xHCI Port Link Info (PORTLI) register.

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 3/4/26 11:42, Michal Pecio wrote:
> On Wed, 19 Nov 2025 16:24:17 +0200, Mathias Nyman wrote:
>> From: "Rai, Amardeep" <amardeep.rai@intel.com>
>>
>> Each xHCI roothub port has a Port Link Info (PORTLI) register that is
>> used by USB3 and eUSB2V2 ports.
>>
>> USB3 ports show link error count, rx lane count, and tx lane count.
>>
>> eUSB2V2 ports show Rx Data Rate (RDR) and Tx Data Rate (TDR).
>>
>> Rx/Tx Data Rate is a multiple of USB2 2.0 HS 480 Mb/s data rates,
>> and is only valid if a eUSB2V2 device is connected (CCS=1).
>>
>> 0 = "USB 2.0 HS" normal HS 480 Mb/s, no eUSB2V2 in use
>> 1 = "HS1" Assymetric eUSB2V2 where this direction runs normal 480Mb/s
>> 2 = "HS2" 960Mb/s
>> ...
>> 10 = "HS10" 4.8 Gb/s, max eUSB2V2 rate
>>
>> PORTLI is Reserved and preserve "RsvdP" for normal USB2 ports
>>
>> Sample output of USB3 port PORTLI:
>> cat /sys/kernel/debug/usb/xhci/0000:00:14.0/ports/port14/portli
>> 0x00000000 LEC=0 RLC=0 TLC=0
>>
>> Signed-off-by: Rai, Amardeep <amardeep.rai@intel.com>
>> Co-developed-by: Mathias Nyman <mathias.nyman@linux.intel.com>
>> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
> 
> Hi,
> 
> This patch causes an oops when there are more port registers counted in
> xhci->max_ports than ports reported by Supported Protocol capabilities.
> On my HW it's due to max_ports being more than maximum port number, but
> it seems that gaps between ports of different speeds are also possible.
> 
>> +static int xhci_portli_show(struct seq_file *s, void *unused)
>> +{
>> +	struct xhci_port	*port = s->private;
>> +	struct xhci_hcd		*xhci = hcd_to_xhci(port->rhub->hcd);
> 
> In such cases port->rhub will be NULL so we can't reach xhci. One
> obvious solution (which works for me) is an explicit NULL check here
> and another seq_printf just for this case, followed by early return.
> 

Thanks for reporting and debugging this.

I was able to fake a similar scenario by leaving out a port in xhci_add_in_port().
It triggered the same oops.

The null pointer check you suggested below fixes it for me. Does it work for you?

diff --git a/drivers/usb/host/xhci-debugfs.c b/drivers/usb/host/xhci-debugfs.c
index c1eb1036ede9..5ff5b761bccf 100644
--- a/drivers/usb/host/xhci-debugfs.c
+++ b/drivers/usb/host/xhci-debugfs.c
@@ -386,11 +386,19 @@ static const struct file_operations port_fops = {
  static int xhci_portli_show(struct seq_file *s, void *unused)
  {
  	struct xhci_port	*port = s->private;
-	struct xhci_hcd		*xhci = hcd_to_xhci(port->rhub->hcd);
+	struct xhci_hcd		*xhci;
  	u32			portli;
  
  	portli = readl(&port->port_reg->portli);
  
+	/* port without protocol capability isn't added to a roothub */
+	if (!port->rhub) {
+		seq_printf(s, "0x%08x\n", portli);
+		return 0;
+	}
+
+	xhci = hcd_to_xhci(port->rhub->hcd);
+
  	/* PORTLI fields are valid if port is a USB3 or eUSB2V2 port */
  	if (port->rhub == &xhci->usb3_rhub)
  		seq_printf(s, "0x%08x LEC=%u RLC=%u TLC=%u\n", portli,

Thanks
Mathias