patch "USB: EHCI: Do not return -EPIPE when hub is disconnected" added to usb-linus

This is a note to let you know that I've just added the patch titled

USB: EHCI: Do not return -EPIPE when hub is disconnected

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 64cc3f12d1c7dd054a215bc1ff9cc2abcfe35832 Mon Sep 17 00:00:00 2001
From: Erkka Talvitie <[email protected]>
Date: Wed, 11 Dec 2019 10:08:39 +0200
Subject: USB: EHCI: Do not return -EPIPE when hub is disconnected

When disconnecting a USB hub that has some child device(s) connected to it (such as a USB mouse), then the stack tries to clear halt and reset device(s) which are _already_ physically disconnected.

The issue has been reproduced with:

CPU: IMX6D5EYM10AD or MCIMX6D5EYM10AE.
SW: U-Boot 2019.07 and kernel 4.19.40.

CPU: HP Proliant Microserver Gen8.
SW: Linux version 4.2.3-300.fc23.x86_64

In this situation there will be error bit for MMF active yet the CERR equals EHCI_TUNE_CERR + halt. Existing implementation interprets this as a stall [1] (chapter 8.4.5).

The possible conditions when the MMF will be active + halt can be found from [2] (Table 4-13).

Fix for the issue is to check whether MMF is active and PID Code is IN before checking for the stall. If these conditions are true then it is not a stall.

What happens after the fix is that when disconnecting a hub with attached device(s) the situation is not interpret as a stall.

[1] [https://www.usb.org/document-library/usb-20-specification, usb_20.pdf]
[2] [https://www.intel.com/content/dam/www/public/us/en/documents/
technical-specifications/ehci-specification-for-usb.pdf]

---
 drivers/usb/host/ehci-q.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

index aa2f77f1506d..8a5c9b3ebe1e 100644
@@ -27,6 +27,10 @@
 
 /*-------------------------------------------------------------------------*/
 
+/* PID Codes that are used here, from EHCI specification, Table 3-16. */
+#define PID_CODE_IN    1
+#define PID_CODE_SETUP 2
+
 /* fill a qtd, returning how much of the buffer we were able to queue up */
 
 static int

@@ -190,7 +194,7 @@ static int qtd_copy_status (
 	int	status = -EINPROGRESS;
 
 	/* count IN/OUT bytes, not SETUP (even short packets) */
-	if (likely (QTD_PID (token) != 2))
+	if (likely(QTD_PID(token) != PID_CODE_SETUP))
 		urb->actual_length += length - QTD_LENGTH (token);
 
 	/* don't modify error codes */

@@ -206,6 +210,13 @@ static int qtd_copy_status (
 		if (token & QTD_STS_BABBLE) {
 			/* FIXME "must" disable babbling device's port too */
 			status = -EOVERFLOW;
+		/*
+		 * When MMF is active and PID Code is IN, queue is halted.
+		 * EHCI Specification, Table 4-13.
+		 */
+		} else if ((token & QTD_STS_MMF) &&
+					(QTD_PID(token) == PID_CODE_IN)) {
+			status = -EPROTO;
 		/* CERR nonzero + halt --> stall */
 		} else if (QTD_CERR(token)) {
 			status = -EPIPE;

2.24.1