From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752953AbcFBHr0 (ORCPT ); Thu, 2 Jun 2016 03:47:26 -0400 Received: from mx2.suse.de ([195.135.220.15]:51765 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752365AbcFBHrY (ORCPT ); Thu, 2 Jun 2016 03:47:24 -0400 Message-ID: <1464853425.2189.3.camel@suse.com> Subject: Re: [RFC PATCHv2] usb: USB Type-C Connector Class From: Oliver Neukum To: Guenter Roeck Cc: Andy Shevchenko , Rajaram R , Felipe Balbi , Heikki Krogerus , Mathias Nyman , Greg KH , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Date: Thu, 02 Jun 2016 09:43:45 +0200 In-Reply-To: <574FD43E.9080305@roeck-us.net> References: <1463661894-22820-1-git-send-email-heikki.krogerus@linux.intel.com> <20160530131951.GA13055@kuha.fi.intel.com> <1464616767.5364.5.camel@suse.com> <20160531083121.GA10084@kuha.fi.intel.com> <1464684509.10800.16.camel@suse.com> <20160531120901.GB10084@kuha.fi.intel.com> <20160531124355.GC10084@kuha.fi.intel.com> <20160531172033.GB14007@roeck-us.net> <20160601082336.GE10084@kuha.fi.intel.com> <1464771866.4051.4.camel@suse.com> <574EE452.3000805@roeck-us.net> <1464848668.8527.2.camel@suse.com> <574FD43E.9080305@roeck-us.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.11 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2016-06-01 at 23:37 -0700, Guenter Roeck wrote: > On 06/01/2016 11:24 PM, Oliver Neukum wrote: > > On Wed, 2016-06-01 at 06:34 -0700, Guenter Roeck wrote: > >> The class code would not explicitly learn about the reset, > >> but it would be informed about the exited modes. > > > > That has drawbacks > > > > Playing devils advocate a bit here > > > - it doesn't tell you what caused the mode to be left (if you > > UFP, it may be the regular command) > > Does it matter ? Potentially yes. Should you restore the last state when the mode is reentered? If it caused the other side to reset, probably not. > > - it is a race against your own command > > It is my understanding that races have to be resolved by the drivers, > since the typec code does not do any locking. This is quite similar > to handling, say, a request to change the vconn source or to change > the power role. Am I missing something ? Yes. There is a fundamental race between Exit Mode and reset if you only report leaving a mode. Drivers can do nothing to prevent it unless reporting resets by themselves. > > - it does not work if you are in basic USB mode > > > Would alternate modes be active in that case ? No and that is the point. A reset happens, presumably because the other side saw an error condition and we just blindly continue because no Alternate Mode was left and our user space remains uninformed. Regards Oliver