linux-kernel - [PATCH v4] usb: host: xhci: Avoid XHCI resume delay if SSUSB device is not present

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Message-ID: <20231011220740.32297-1-quic_wcheng@quicinc.com>
Date:   Wed, 11 Oct 2023 15:07:40 -0700
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     <mathias.nyman@...el.com>, <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        Wesley Cheng <quic_wcheng@...cinc.com>
Subject: [PATCH v4] usb: host: xhci: Avoid XHCI resume delay if SSUSB device is not present

There is a 120ms delay implemented for allowing the XHCI host controller to
detect a U3 wakeup pulse.  The intention is to wait for the device to retry
the wakeup event if the USB3 PORTSC doesn't reflect the RESUME link status
by the time it is checked.  As per the USB3 specification:

  tU3WakeupRetryDelay ("Table 7-12. LTSSM State Transition Timeouts")

This would allow the XHCI resume sequence to determine if the root hub
needs to be also resumed.  However, in case there is no device connected,
or if there is only a HSUSB device connected, this delay would still affect
the overall resume timing.

Since this delay is solely for detecting U3 wake events (USB3 specific)
then ignore this delay for the disconnected case and the HSUSB connected
only case.

Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
---
Depends-on:
https://lore.kernel.org/linux-usb/20230915143108.1532163-3-mathias.nyman@linux.intel.com/

changes in v4:
- Added change log between versions

changes in v3:
- Modified logic to determine if a USB3.0 device is connected.  Using the suspended_ports
and bus_suspended bitmasks.  suspended_port is non-zero as ports are runtime suspended,
while bus_suspended is non-zero if system suspend occurs while ports are active.

changes in v2:
- Looping across portsc to determine if there is a valid USB3 connection.

 drivers/usb/host/xhci.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index e1b1b64a0723..1855cab1be56 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -805,6 +805,18 @@ static void xhci_disable_hub_port_wake(struct xhci_hcd *xhci,
 	spin_unlock_irqrestore(&xhci->lock, flags);
 }
 
+/*
+ * Utilize suspended_ports and bus_suspended to determine if USB3 device is
+ * connected.  The bus state bits are set by XHCI hub when root hub udev is
+ * suspended.  Used to determine if USB3 remote wakeup considerations need to
+ * be accounted for during XHCI resume.
+ */
+static bool xhci_usb3_dev_connected(struct xhci_hcd *xhci)
+{
+	return !!xhci->usb3_rhub.bus_state.suspended_ports ||
+		!!xhci->usb3_rhub.bus_state.bus_suspended;
+}
+
 static bool xhci_pending_portevent(struct xhci_hcd *xhci)
 {
 	struct xhci_port	**ports;
@@ -968,6 +980,7 @@ int xhci_resume(struct xhci_hcd *xhci, pm_message_t msg)
 	int			retval = 0;
 	bool			comp_timer_running = false;
 	bool			pending_portevent = false;
+	bool			usb3_connected = false;
 	bool			reinit_xhc = false;
 
 	if (!hcd->state)
@@ -1116,9 +1129,14 @@ int xhci_resume(struct xhci_hcd *xhci, pm_message_t msg)
 		 * Resume roothubs only if there are pending events.
 		 * USB 3 devices resend U3 LFPS wake after a 100ms delay if
 		 * the first wake signalling failed, give it that chance.
+		 * Avoid this check if there are no devices connected to
+		 * the SS root hub. (i.e. HS device connected or no device
+		 * connected)
 		 */
 		pending_portevent = xhci_pending_portevent(xhci);
-		if (!pending_portevent && msg.event == PM_EVENT_AUTO_RESUME) {
+		usb3_connected = xhci_usb3_dev_connected(xhci);
+		if (!pending_portevent && usb3_connected &&
+		     msg.event == PM_EVENT_AUTO_RESUME) {
 			msleep(120);
 			pending_portevent = xhci_pending_portevent(xhci);
 		}