linux-kernel - [PATCH 5/6] usb: xhci: Avoid Stop Endpoint retry loop if the endpoint seems Running

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Message-ID: <20250310094129.20273c14@foxbook>
Date: Mon, 10 Mar 2025 09:41:29 +0100
From: Michal Pecio <michal.pecio@...il.com>
To: Mathias Nyman <mathias.nyman@...el.com>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>
Cc: linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 5/6] usb: xhci: Avoid Stop Endpoint retry loop if the
 endpoint seems Running

Nothing prevents a broken HC from claiming that an endpoint is Running
and repeatedly rejecting Stop Endpoint with Context State Error.

Avoid infinite retries and give back cancelled TDs.

No such cases known so far, but HCs have bugs.

Signed-off-by: Michal Pecio <michal.pecio@...il.com>
---
 drivers/usb/host/xhci-ring.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 28ebc0fc5bc2..241cd82672a6 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1259,16 +1259,19 @@ static void xhci_handle_cmd_stop_ep(struct xhci_hcd *xhci, int slot_id,
 			 * Stopped state, but it will soon change to Running.
 			 *
 			 * Assume this bug on unexpected Stop Endpoint failures.
-			 * Keep retrying until the EP starts and stops again, on
-			 * chips where this is known to help. Wait for 100ms.
+			 * Keep retrying until the EP starts and stops again.
 			 */
-			if (time_is_before_jiffies(ep->stop_time + msecs_to_jiffies(100)))
-				break;
 			fallthrough;
 		case EP_STATE_RUNNING:
 			/* Race, HW handled stop ep cmd before ep was running */
 			xhci_dbg(xhci, "Stop ep completion ctx error, ctx_state %d\n",
 					GET_EP_CTX_STATE(ep_ctx));
+			/*
+			 * Don't retry forever if we guessed wrong or a defective HC never starts
+			 * the EP or says 'Running' but fails the command. We must give back TDs.
+			 */
+			if (time_is_before_jiffies(ep->stop_time + msecs_to_jiffies(100)))
+				break;
 
 			command = xhci_alloc_command(xhci, false, GFP_ATOMIC);
 			if (!command) {
-- 
2.48.1