Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752112AbdCCTGZ (ORCPT ); Fri, 3 Mar 2017 14:06:25 -0500 Received: from bh-25.webhostbox.net ([208.91.199.152]:51320 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751797AbdCCTGX (ORCPT ); Fri, 3 Mar 2017 14:06:23 -0500 Subject: Re: [PATCH v17 2/3] usb: USB Type-C connector class To: Heikki Krogerus , Mats Karrman References: <20170221142405.76299-1-heikki.krogerus@linux.intel.com> <20170221142405.76299-3-heikki.krogerus@linux.intel.com> <4b4bbffc-db02-3b54-04bc-e7de79b2d9ed@roeck-us.net> <07618170-d561-e7fe-08e0-91316c53d832@gmail.com> <20170303125940.GA6999@kuha.fi.intel.com> Cc: Greg KH , Felipe Balbi , Oliver Neukum , linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org From: Guenter Roeck Message-ID: Date: Fri, 3 Mar 2017 06:49:54 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <20170303125940.GA6999@kuha.fi.intel.com> Content-Type: text/plain; charset=windows-1252; 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 Content-Length: 5260 Lines: 106 On 03/03/2017 04:59 AM, Heikki Krogerus wrote: > Hi, > > On Fri, Mar 03, 2017 at 08:29:18AM +0100, Mats Karrman wrote: >> On 2017-03-03 04:13, Guenter Roeck wrote: >> >>> On 03/02/2017 07:22 AM, Mats Karrman wrote: >>>> .... >>>> Looking forward, one thing I have run into is how to connect the typec driver with a >>>> driver for an alternate mode. E.g. the DisplayPort Alternate Mode specification >>>> includes the HPD (hot plug) and HPD-INT (hot plug interrupt) signals as bits in the >>>> Attention message. These signals are needed by the DisplayPort driver to know when to >>>> start negotiation etc. >>>> Have you got any thoughts on how to standardize such interfaces? > > My idea was to have something like the altmode "bus" at one point. > We create a device for every alternate mode registered in typec class, > so the alternate modes registered for the ports and partners would > simply be attached to the altmode bus. There would be a bus per port > of course. > > The drivers for the port alternate modes would take care of things > like muxing and other platform specific stuff as needed, and they > would be tied to the underlying subsystems and drivers, graphics in > case of DisplayPort. The drivers for the partner alternate modes would > take care of the actual communication with the alternate mode with > VDMs if needed (but not necessarily), and they would need to be tied > to the port alternate modes. In practice the driver for both the port > and the partner alternate modes will be the same (in the same > location) obviously, at least in most cases. > > I think a bus would allow us to support several ways of handling the > alternate modes on different platforms. It would work fine also on > platforms that had no use for it of course, like platforms where > firmware or EC takes care of most things related to Type-C. > > But please note that since this is just a high level idea still, we > wouldn't for example need to create an actual bus if there is no use > for it, but since we have the SVIDs that can be used for matching, > then why not try take advantage of them, right. > > How would something like that sound to you guys? > >>> That really depends on the lower level driver. For Chromebooks, where the Type-C >>> Protocol Manager runs on the EC, we have an extcon driver which reports the pin states >>> to the graphics drivers and connects to the Type-C class code using the Type-C class >>> API. I still need to update, re-test, and publish that code. The published code in >>> https://chromium.googlesource.com/chromiumos/third_party/kernel/, branch chromeos-4.4, >>> shows how it can be done, though that code currently still uses the Android Type-C >>> infrastructure. > > In this case I think you would only need to register a driver with the > bus in case you want the handle to the device for the alternate mode. > >> OK, thanks! >> >> My system is a bit different. It's an i.MX6 SoC with the typec phy and DP controller connected >> directly to the SoC and it's using DTB/OF. > > Is this "DP controller" a controller that is capable of taking care of > the USB Power Delivery communication with the partner regarding > DisplayPort alternate mode? > >> Using extcon I would have a driver that is both typec class and extcon driver at the same time >> since I can't share the access to the typec phy. Is this done elsewhere in the kernel? >> I don't know much about the wcove PMIC and what alternate modes it might support but I >> guess that driver would end up in the same place. > > What alternate modes systems with WhiskeyCove supports depends on > the platform. WhiskeyCove PMIC (as in Power Management IC) is > available on a few Intel Atom platforms. The USB Type-C PHY in it > provides a simple USB PD transceiver that does not touch the actual > communication with the partners. The communication needs to be done in > software, including dealing with alternate modes. > > I'm not planning on using extcon for anything with WhiskeyCove. I > don't have any use for it. It looks to me that extcon is used just as > a tool to create software couplings in many cases, and I'm not > completely comfortable with that. > For rk3399 we went back and forth trying other approaches, but using extcon turned out to be the most straightforward mechanism; everything else would just have replicated what extcon already provides. Having said that, I am open to other approaches. The rk3399 implementation may be seen as an example on what is required, specifically when it comes to the interaction between cable, DP, and the Type-C phy. Guenter > In my case with DP altmode, if we had for example muxes to take care > of, I don't think it would be a problem to tie the driver for the mux > to the graphics directly, so basically make it part of the graphics > stack. That driver would be the port (and partner) altmode driver. > >> Do we need to further standardize attributes under (each) specific alternate mode to >> include things such as HPD for the DP mode? > > I'm not completely sure what kind of system you have, but I would > imagine that if we had the bus, your DP controller driver would be the > port (and partner) alternate mode driver. The bus would bind you to > the typec phy. > > > Thanks, >