From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932654AbcFBKTB (ORCPT ); Thu, 2 Jun 2016 06:19:01 -0400 Received: from mga02.intel.com ([134.134.136.20]:53942 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932510AbcFBKS7 (ORCPT ); Thu, 2 Jun 2016 06:18:59 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,405,1459839600"; d="scan'208";a="820117642" Date: Thu, 2 Jun 2016 13:18:53 +0300 From: Heikki Krogerus To: Guenter Roeck Cc: Oliver Neukum , Andy Shevchenko , Rajaram R , Felipe Balbi , Mathias Nyman , Greg KH , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Subject: Re: [RFC PATCHv2] usb: USB Type-C Connector Class Message-ID: <20160602101853.GC25305@kuha.fi.intel.com> References: <1463661894-22820-1-git-send-email-heikki.krogerus@linux.intel.com> <1464773169.4051.8.camel@suse.com> <20160601232926.GA8463@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160601232926.GA8463@roeck-us.net> User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 01, 2016 at 04:29:26PM -0700, Guenter Roeck wrote: > On Wed, Jun 01, 2016 at 11:26:09AM +0200, Oliver Neukum wrote: > > On Thu, 2016-05-19 at 15:44 +0300, Heikki Krogerus wrote: > > > Just noticed that the "active" file is for now read only, but it needs > > > to be changed to writable. That file will of course provide means for > > > the userspace to Exit and Enter modes. But please note that the > > > responsibility of the dependencies between the modes, say, if a plug > > > needs to be in one mode or the other in order for the partner to enter > > > some specific mode, will fall on the Alternate Mode specific drivers > > > once we have the altmode bus. I remember there were concerns about > > > this in the original thread. > > > > There's one thing we haven't touched upon yet. And I cannot really find > > an answer in the spec. > > > > What do we do if we return from S4 or S3? I think we need to restore > > the ALternate Mode because our display may be running over that > > Alternate Mode. > > If we want to support USB persist we also need to restore data role > > after S4. > > > I don't have an answer ... but another interesting question. > > How do we distinguish between alternate modes supported by a host vs. > alternate modes supported by a sink ? typec_capability includes a pointer > to alternate modes supportedf by the connector, but it is not clear if > those are alternate modes supported as host, or alternate modes supported > as device, or alternate modes supported by both. > > This doesn't matter much if only a fixed role is supported, but it does matter > for dual role ports. A laptop will typically only support DisplayPort as host, > for example. The DP alternate mode spec actually separates the display role from Type-C role. A laptop most likely would only support the modes for display host roles, but if the port was DRP port then it would still do so in both Type-C roles. So basically, even if the display was Type-C host, it would still work as a display when attached to the laptop. > Any idea ? I'm actually not sure this is a problem. Thanks, -- heikki