From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751950AbcFUUtc (ORCPT ); Tue, 21 Jun 2016 16:49:32 -0400 Received: from mx2.suse.de ([195.135.220.15]:35191 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751537AbcFUUtT (ORCPT ); Tue, 21 Jun 2016 16:49:19 -0400 Message-ID: <1466541785.2014.16.camel@suse.com> Subject: Re: [RFC PATCHv2] usb: USB Type-C Connector Class From: Oliver Neukum To: Heikki Krogerus Cc: Andy Shevchenko , Rajaram R , Felipe Balbi , Mathias Nyman , Greg KH , Guenter Roeck , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org Date: Tue, 21 Jun 2016 22:43:05 +0200 In-Reply-To: <20160621135845.GA10715@kuha.fi.intel.com> References: <1463661894-22820-1-git-send-email-heikki.krogerus@linux.intel.com> <1466514532.2091.5.camel@suse.com> <20160621135845.GA10715@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 Tue, 2016-06-21 at 16:58 +0300, Heikki Krogerus wrote: > On Tue, Jun 21, 2016 at 03:08:52PM +0200, Oliver Neukum wrote: > > > The firmware will surely want to display something. So it is possible > > that we start the OS will a valid power contract. How do we deal > > with that? Renegotiate? > > Systems where the firmware has to negotiate PD will likely provide > firmware interface like UCSI, and where the OS has no direct > interaction with the USB PD transceiver. In these case there is no > need to renegotiate as we are just reporting in OS the initial state > after bootup. How certain is that? I was under the impression that on many systems the OS would speak to the TCPM directly. > We do have a system where the typec port is used to power the board. > On these systems the firmware does not communicate PD (so we will > never have the firmware displaying anything over Type-C on those > systems), but the USB PD chargers for example are detected as 3.0A > Type-C power supplies before any USB PD negotiation takes place, just > like the spec says, and that is more then enough to power these boards. Now correct me, if I am misreading the spec. I am sure the system will boot unless it needs ridiculous amounts of power, but will we see anything on the screen? As far as I can tell the spec actually says that you cannot enter an alternate mode without having established a power contract. If we really leave entering modes up to user space, we have lost printk before getting into the initrd at the earliest. Regards Oliver