From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754575AbaEBQGg (ORCPT ); Fri, 2 May 2014 12:06:36 -0400 Received: from mga03.intel.com ([143.182.124.21]:27756 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754553AbaEBQGd (ORCPT ); Fri, 2 May 2014 12:06:33 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,973,1389772800"; d="scan'208";a="525023568" Date: Sat, 3 May 2014 00:05:41 -0400 From: Zhuang Jin Can To: Felipe Balbi Cc: linux-usb@vger.kernel.org, linux-omap@vger.kernel.org, linux-kernel@vger.kernel.org, David Cohen Subject: Re: [PATCH] usb: dwc3: gadget: giveback request if start transfer fail Message-ID: <20140503040541.GC19925@intel.com> Reply-To: jin.can.zhuang@intel.com References: <20140501063608.GA30575@intel.com> <20140430195829.GA3839@saruman.home> <20140501204452.GD30575@intel.com> <20140501151328.GB6355@saruman.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140501151328.GB6355@saruman.home> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Thu, May 01, 2014 at 10:13:28AM -0500, Felipe Balbi wrote: > On Thu, May 01, 2014 at 04:44:52PM -0400, Zhuang Jin Can wrote: > > On Wed, Apr 30, 2014 at 02:58:29PM -0500, Felipe Balbi wrote: > > > On Thu, May 01, 2014 at 02:36:08AM -0400, Zhuang Jin Can wrote: > > > > At least we should giveback the current request to the > > > > gadget. Otherwise, the gadget will be stuck without knowing > > > > anything. > > > > > > > > It was oberved that the failure can happen if the request is > > > > queued when the run/stop bit of controller is not set. > > > > > > why is your gadget queueing any requests before calling ->udc_start() ? > > > > > > A better question, what modification have you done to udc-core.c which > > > broke this ? udc-core *always* calls ->udc_start() by the time you load > > > a gadget driver so this case will *never* happen. Whatever modification > > > you did, broke this assumption and I will *not* accept this patch > > > because the bug is elsewhere and *not* in mainline kernel. > > > > > It's found in Android using kernel 3.10.20. Android has its own > > usb_composite_driver usb/gadget/android.c (not in mainline), and it > > so you found something on an old kernel using an out-of-tree gadget > driver. > > > allows userspace to disconnect the pullup (i.e clear run/stop bit in dwc3) > > and remove the gadget functions like adb, mtp and then add new functions > > like rndis, acm. The problem is when you disconnect the pullup, a gadget > > maybe in the middle of queuing a request, and result in the "start > > transfer cmd failure". I think this is also a common issue for other > > Android gadget needs to learn how to cope with that. > Agree. > > usb_composite_drivers too. Normally, if one of the gadget deactivate its > > own function, the pullup will be disconnected, other gadgets won't get > > notified until their requests are failed. So it makes dwc3 more robust > > to deal with these situations. > > Right, but Android gadget can run on top of several other UDCs and you > want to have a single one of them cope with android's bug ? > > You'd be better off getting google to accept a bugfix to the android > gadget, since that's where the problem lies. > I agree. I'll try to push the fix to google. It's really hard to fix the race condition (for me), as any gadget or /sys/class/udc/soft_connect can just disconnect the pullup anytime they want. The only thing I can do is giving back the request to the gadget if the condition happens. Jincan