From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754647AbcK1K0a (ORCPT ); Mon, 28 Nov 2016 05:26:30 -0500 Received: from mx2.suse.de ([195.135.220.15]:37166 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932575AbcK1KZg (ORCPT ); Mon, 28 Nov 2016 05:25:36 -0500 Message-ID: <1480328372.22547.8.camel@suse.com> Subject: Re: [PATCHv12 2/3] usb: USB Type-C connector class From: Oliver Neukum To: Heikki Krogerus Cc: Guenter Roeck , Badhri Jagan Sridharan , Greg KH , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Date: Mon, 28 Nov 2016 11:19:32 +0100 In-Reply-To: <20161124095755.GB17492@kuha.fi.intel.com> References: <20161122141147.21977-1-heikki.krogerus@linux.intel.com> <20161122141147.21977-3-heikki.krogerus@linux.intel.com> <20161124095755.GB17492@kuha.fi.intel.com> 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 Thu, 2016-11-24 at 11:57 +0200, Heikki Krogerus wrote: > On Wed, Nov 23, 2016 at 09:12:04PM -0800, Guenter Roeck wrote: > > In our implementation, the default preferred role is determined by the > > low level driver (as, in my understanding, is suggested by the standard). > > This means that the ABI will report "no preferred role", unless user space > > overwrites it, even though there _is_ in fact a preferred role, and the > > low level driver will execute try.src or try.snk based on that role. > > I'm not sure which standard are you referring? Try.SNK and Try.SRC are > optional mechanisms for *policy-based* role preference according to > the USB Type-C spec. The policy really should always come from the Not all that obvious. If you are looking at it from a distro view point if you know that you are booting on basically a gadget, you'll be happy to take the hint. And if the hardware knows it is better as a sink or source, we should take the hint. > user space in our case, but I don't think that rules out for example > initial role preferences coming from the lower level drivers. Indeed. That should not be a hindrance to submission and inclusion. > We will need a way the OS can set the initial preference for every > port. Note that once we can support that, what ever the lower level > drivers request will be overridden by it. So if for example the > platform has preference for an initial role, we will simply ignore it > if the policy says otherwise. Again, not obvious in a distro. I would actually prefer a module parameter that would allow us to prefer try.src, as we know how to be a master. None of that should hinder submission and inclusion. Regards Oliver