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On Fri, Nov 26, 2021 at 11:30 PM Alan Stern [off-list ref] wrote:

On Fri, Nov 26, 2021 at 07:56:51PM +0800, Kai-Heng Feng wrote:

quoted

Unplugging USB device may cause an incorrect warm reset loop:
[  143.039019] xhci_hcd 0000:00:14.0: Port change event, 2-3, id 19, portsc: 0x4202c0
[  143.039025] xhci_hcd 0000:00:14.0: handle_port_status: starting usb2 port polling.
[  143.039051] hub 2-0:1.0: state 7 ports 10 chg 0000 evt 0008
[  143.039058] xhci_hcd 0000:00:14.0: Get port status 2-3 read: 0x4202c0, return 0x4102c0
[  143.039092] xhci_hcd 0000:00:14.0: clear port3 connect change, portsc: 0x4002c0
[  143.039096] usb usb2-port3: link state change
[  143.039099] xhci_hcd 0000:00:14.0: clear port3 link state change, portsc: 0x2c0
[  143.039101] usb usb2-port3: do warm reset
[  143.096736] xhci_hcd 0000:00:14.0: Get port status 2-3 read: 0x2b0, return 0x2b0
[  143.096751] usb usb2-port3: not warm reset yet, waiting 50ms
[  143.131500] xhci_hcd 0000:00:14.0: Can't queue urb, port error, link inactive
[  143.138260] xhci_hcd 0000:00:14.0: Port change event, 2-3, id 19, portsc: 0x2802a0
[  143.138263] xhci_hcd 0000:00:14.0: handle_port_status: starting usb2 port polling.
[  143.160756] xhci_hcd 0000:00:14.0: Get port status 2-3 read: 0x2802a0, return 0x3002a0
[  143.160798] usb usb2-port3: not warm reset yet, waiting 200ms

The warm reset is due to its PLS is in eSS.Inactive state. However, USB
3.2 spec table 10-13 mentions "Ports can be disabled by either a fault
condition (disconnect event or other fault condition)", xHCI 1.2 spec
table 5-27 also states that "This flag shall automatically be cleared to
‘0’ by a disconnect event or other fault condition." on PED.

So use CSC = 0 and PED = 0 as indication that device is disconnecting to
avoid doing warm reset.

Signed-off-by: Kai-Heng Feng <redacted>
---
v2:
 - Change the variable type to bool.

 drivers/usb/core/hub.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index a9a04ea967019..4f081df70ecf2 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c

@@ -5564,6 +5564,7 @@ static void port_event(struct usb_hub *hub, int port1)
              __must_hold(&port_dev->status_lock)
 {
      int connect_change;
+     bool disconnect = false;
      struct usb_port *port_dev = hub->ports[port1 - 1];
      struct usb_device *udev = port_dev->child;
      struct usb_device *hdev = hub->hdev;

@@ -5579,6 +5580,9 @@ static void port_event(struct usb_hub *hub, int port1)
      if (portchange & USB_PORT_STAT_C_CONNECTION) {
              usb_clear_port_feature(hdev, port1, USB_PORT_FEAT_C_CONNECTION);
              connect_change = 1;
+             if (!(portstatus & USB_PORT_STAT_CONNECTION) &&
+                 !(portstatus & USB_PORT_STAT_ENABLE))
+                     disconnect = true;
      }

This looks a little strange.  Can there ever be a situation where
PORT_STAT_CONNECTION is off and PORT_STAT_ENABLE is on?  (It's not allowed in
USB-2.)

Right, the spec only states PORT_STAT_ENABLE = 0. Will change that in
next revision.

quoted

      if (portchange & USB_PORT_STAT_C_ENABLE) {

@@ -5647,7 +5651,7 @@ static void port_event(struct usb_hub *hub, int port1)
       * Warm reset a USB3 protocol port if it's in
       * SS.Inactive state.
       */
-     if (hub_port_warm_reset_required(hub, port1, portstatus)) {
+     if (hub_port_warm_reset_required(hub, port1, portstatus) && !disconnect) {
              dev_dbg(&port_dev->dev, "do warm reset\n");
              if (!udev || !(portstatus & USB_PORT_STAT_CONNECTION)
                              || udev->state == USB_STATE_NOTATTACHED) {

Why is it correct to skip doing a warm reset on a disconnected port here, but not
correct to skip doing a warm reset on a disconnected port in all the other places
where hub_port_warm_reset_required() gets called?

Can a disconnect event happens to other places other than port_event()?

Kai-Heng

Alan Stern