xhci: Add a flag to disable USB3 lpm on a xhci root port level.

One USB3 roothub port may support link power management, while another
root port on the same xHC can't due to different retimers used for
the ports.

This is the case with Intel Alder Lake, and possible future platforms
where retimers used for USB4 ports cause too long exit latecy to
enable native USB3 lpm U1 and U2 states.

Add a flag in the xhci port structure to indicate if the port is
lpm_incapable, and check it while calculating exit latency.

Cc: [email protected]
Signed-off-by: Mathias Nyman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: matnyman

drivers/usb/host/xhci.c

@@ -5049,6 +5049,7 @@ static int xhci_enable_usb3_lpm_timeout(struct usb_hcd *hcd,
 			struct usb_device *udev, enum usb3_link_state state)
 {
 	struct xhci_hcd	*xhci;
+	struct xhci_port *port;
 	u16 hub_encoded_timeout;
 	int mel;
 	int ret;
@@ -5065,6 +5066,13 @@ static int xhci_enable_usb3_lpm_timeout(struct usb_hcd *hcd,
 	if (xhci_check_tier_policy(xhci, udev, state) < 0)
 		return USB3_LPM_DISABLED;
 
+	/* If connected to root port then check port can handle lpm */
+	if (udev->parent && !udev->parent->parent) {
+		port = xhci->usb3_rhub.ports[udev->portnum - 1];
+		if (port->lpm_incapable)
+			return USB3_LPM_DISABLED;
+	}
+
 	hub_encoded_timeout = xhci_calculate_lpm_timeout(hcd, udev, state);
 	mel = calculate_max_exit_latency(udev, state, hub_encoded_timeout);
 	if (mel < 0) {

drivers/usb/host/xhci.h

@@ -1735,6 +1735,7 @@ struct xhci_port {
 	int			hcd_portnum;
 	struct xhci_hub		*rhub;
 	struct xhci_port_cap	*port_cap;
+	unsigned int		lpm_incapable:1;
 };
 
 struct xhci_hub {