[PATCH v2] xhci: Set port link to RxDetect if port is not enabled after resume

[Kai-Heng Feng <kai.heng.feng@canonical.com>]

On Dell TB16, Realtek USB ethernet (r8152) connects to an SMSC hub which
then connects to ASMedia xHCI's root hub:

/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 5000M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/7p, 5000M
            |__ Port 2: Dev 3, If 0, Class=Vendor Specific Class, Driver=r8152, 5000M

Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 004 Device 002: ID 0424:5537 Standard Microsystems Corp. USB5537B
Bus 004 Device 003: ID 0bda:8153 Realtek Semiconductor Corp. RTL8153 Gigabit Ethernet Adapter

The port is disabled after resume:
xhci_hcd 0000:3f:00.0: Get port status 4-1 read: 0x280, return 0x280

According to xHCI 4.19.1.2.1, we should set link to RxDetect to transit
it from disabled state to disconnected state, which allows the port to
be set to U0 and completes the resume process.

My own test shows port can still resume when it's not enabled, as long
as its link is in U states. So constrain the new logic only when link is
not in any U state.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
---
 drivers/usb/host/xhci-hub.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
index a9c87eb8951e..263f9a9237a1 100644
--- a/drivers/usb/host/xhci-hub.c
+++ b/drivers/usb/host/xhci-hub.c
@@ -1776,6 +1776,14 @@ int xhci_bus_resume(struct usb_hcd *hcd)
 			clear_bit(port_index, &bus_state->bus_suspended);
 			continue;
 		}
+
+		/* 4.19.1.2.1 */
+		if (!(portsc & PORT_PE) && (portsc & PORT_PLS_MASK) > XDEV_U3) {
+			portsc = xhci_port_state_to_neutral(portsc);
+			portsc &= ~PORT_PLS_MASK;
+			portsc |= PORT_LINK_STROBE | XDEV_RXDETECT;
+		}
+
 		/* resume if we suspended the link, and it is still suspended */
 		if (test_bit(port_index, &bus_state->bus_suspended))
 			switch (portsc & PORT_PLS_MASK) {
-- 
2.17.1