linux-kernel - [PATCH v2] usb: host: xhci: Avoid XHCI resume delay if SSUSB device is not present

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Message-ID: <20230901001518.25403-1-quic_wcheng@quicinc.com>
Date:   Thu, 31 Aug 2023 17:15:18 -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>,
        <quic_jackp@...cinc.com>, Wesley Cheng <quic_wcheng@...cinc.com>
Subject: [PATCH v2] 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>
---
 drivers/usb/host/xhci.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index e1b1b64a0723..640db6a4e686 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -805,6 +805,24 @@ static void xhci_disable_hub_port_wake(struct xhci_hcd *xhci,
 	spin_unlock_irqrestore(&xhci->lock, flags);
 }
 
+static bool xhci_usb3_dev_connected(struct xhci_hcd *xhci)
+{
+	struct xhci_port	**ports;
+	int			port_index;
+	u32			portsc;
+
+	port_index = xhci->usb3_rhub.num_ports;
+	ports = xhci->usb3_rhub.ports;
+
+	while (port_index--) {
+		portsc = readl(ports[port_index]->addr);
+		if (portsc & (portsc & PORT_CONNECT))
+			return true;
+	}
+
+	return false;
+}
+
 static bool xhci_pending_portevent(struct xhci_hcd *xhci)
 {
 	struct xhci_port	**ports;
@@ -968,6 +986,7 @@ 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 +1135,14 @@ 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);
 		}