linux-kernel - [PATCH] usbcore: fix BABBLE failed enumeration of legacy USB2 devices on USB3 bus

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Date:	Tue, 24 Dec 2013 04:19:18 +0000
From:	"Marius  Silaghi" <msilaghi@....edu>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
CC:	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Lan Tianyu <tianyu.lan@...el.com>,
	"Xenia Ragiadakou" <burzalodowa@...il.com>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
	Jiri Kosina <trivial@...nel.org>
Subject: [PATCH] usbcore: fix BABBLE failed enumeration of legacy USB2
 devices on USB3 bus

From: Marius C Silaghi <msilaghi@....edu>

This patch is generated against the last kernel version in the github kernel repository.
Some older families of USB2 cameras (STC-XXXXXUSB) do not support querying only the first 8 bytes of their 
device descriptor and therefore fail at enumeration on USB3 HCDs, with babble error -75 as they send more than
the expected 8 bytes. The proposed patch extends the mechanism used for non USB3 HCDs in the first part of 
the same function, and  successively tries to query both the 8 byte prefix of the device descriptor, as well as 
the whole device descriptor (in case the old style query of the 8 byte prefix fails).
In fact, for the cameras I try to fix, the preferred condition is the negation of the one in the proposed patch,  
"if (!USE_NEW_SCHEME(retry_counter))", to try first the version successful on this case, but I keep the 
current order of the "if" branches to ensure clean continuation of support for other supported devices.

Signed-off-by: Marius C Silaghi <msilaghi@....edu>
---
--- linux/drivers/usb/core/hub.c.orig	2013-12-23 22:09:50.545093470 -0500
+++ linux/drivers/usb/core/hub.c	2013-12-23 22:29:40.521043702 -0500
@@ -4197,7 +4197,19 @@ hub_port_init (struct usb_hub *hub, stru
 				break;
 		}

-		retval = usb_get_device_descriptor(udev, 8);
+		/*  Try first the old 8-byte query (since it may be expected
+		 *  by some devices), but then give at least a chance to the
+		 *  new form (retrieving the whole descriptor)!
+		 *  Querying the content of the whole structure is required
+		 *  for older USB2 video cameras which do not support partial
+		 *  descriptor queries, like the STC-XXXUSB family.
+		 *  Windows also supports them.
+		 */
+		if (USE_NEW_SCHEME(retry_counter))
+			retval = usb_get_device_descriptor(udev, 8);
+		else
+			retval = usb_get_device_descriptor(udev,
+				       sizeof(struct usb_device_descriptor));
 		if (retval < 8) {
 			if (retval != -ENODEV)
 				dev_err(&udev->dev,

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