From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754511AbdEQJgt (ORCPT ); Wed, 17 May 2017 05:36:49 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:39930 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751759AbdEQJgq (ORCPT ); Wed, 17 May 2017 05:36:46 -0400 Subject: Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers To: Oliver Neukum , Badhri Jagan Sridharan , Heikki Krogerus , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org References: <20170517073219.8315-1-Badhri@google.com> <1495006472.30577.6.camel@suse.com> From: Guenter Roeck Message-ID: <2b7e6715-35b8-0d4a-fb28-3a59bd72916e@roeck-us.net> Date: Wed, 17 May 2017 02:36:44 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <1495006472.30577.6.camel@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: linux@roeck-us.net X-Authenticated-Sender: bh-25.webhostbox.net: linux@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanks, Guenter