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

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Message-ID: <20230427190145.4623-1-quic_wcheng@quicinc.com>
Date:   Thu, 27 Apr 2023 12:01:45 -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] 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 | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 78790dc13c5f..7a86cd683502 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -834,7 +834,8 @@ static bool xhci_pending_portevent(struct xhci_hcd *xhci)
 	while (port_index--) {
 		portsc = readl(ports[port_index]->addr);
 		if (portsc & PORT_CHANGE_MASK ||
-		    (portsc & PORT_PLS_MASK) == XDEV_RESUME)
+		    (portsc & PORT_PLS_MASK) == XDEV_RESUME ||
+		    !(portsc & PORT_CONNECT))
 			return true;
 	}
 	return false;
@@ -1114,6 +1115,9 @@ int xhci_resume(struct xhci_hcd *xhci, bool hibernated)
 		 * 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) {