From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755524AbdERJPY (ORCPT ); Thu, 18 May 2017 05:15:24 -0400 Received: from mx2.suse.de ([195.135.220.15]:37368 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754890AbdERJPW (ORCPT ); Thu, 18 May 2017 05:15:22 -0400 Message-ID: <1495098831.6672.2.camel@suse.com> Subject: Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers From: Oliver Neukum To: Guenter Roeck , Badhri Jagan Sridharan , Heikki Krogerus , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Date: Thu, 18 May 2017 11:13:51 +0200 In-Reply-To: <2b7e6715-35b8-0d4a-fb28-3a59bd72916e@roeck-us.net> References: <20170517073219.8315-1-Badhri@google.com> <1495006472.30577.6.camel@suse.com> <2b7e6715-35b8-0d4a-fb28-3a59bd72916e@roeck-us.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.20.5 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 Am Mittwoch, den 17.05.2017, 02:36 -0700 schrieb Guenter Roeck: > On 05/17/2017 12:34 AM, Oliver Neukum wrote: > > > > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan > > Sridharan: > > > > Hi, > > > > > > > > "Two independent set of mechanisms are defined to allow a USB Type-C > > > DRP to functionally swap power and data roles. When USB PD is > > > supported, power and data role swapping is performed as a subsequent > > > step following the initial connection process. For non-PD implementations, > > > power/data role swapping can optionally be dealt with as part of the initial > > > connection process." > > > > Well, as I read it, without PD once a connection is established, you > > are stuck with your role. So it seems to me that blocking a later > > attempt to change it makes sense. > > > > That seems to be a harsh and not very user friendly reading of the specification. > > I would argue that the user doesn't care if the partner supports PD or not > when selecting a role, and I would prefer to provide an implementation which is > as user friendly as possible. Data role, no question, you are right. Power role is a different question. A switch of power role with PD should not lead to a disconnect. Any other method might. So equating them does not look like a good idea. Regards Oliver