From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1946050AbcBRKh7 (ORCPT ); Thu, 18 Feb 2016 05:37:59 -0500 Received: from mail-wm0-f68.google.com ([74.125.82.68]:33862 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1425611AbcBRKh4 (ORCPT ); Thu, 18 Feb 2016 05:37:56 -0500 MIME-Version: 1.0 In-Reply-To: <20160217142816.GC24649@kuha.fi.intel.com> References: <20160211135011.GA32213@kuha.fi.intel.com> <1455550218.22176.11.camel@suse.com> <20160216092238.GA18565@kuha.fi.intel.com> <1455629987.4532.25.camel@suse.com> <20160217075841.GA24649@kuha.fi.intel.com> <1455699834.7626.4.camel@suse.com> <87fuwrsk7w.fsf@ti.com> <1455705412.7626.18.camel@suse.com> <20160217111116.GB24649@kuha.fi.intel.com> <87bn7fihld.fsf@ti.com> <20160217142816.GC24649@kuha.fi.intel.com> Date: Thu, 18 Feb 2016 16:07:54 +0530 Message-ID: Subject: Re: [PATCH 2/3] usb: type-c: USB Type-C Connector System Software Interface From: Rajaram R To: Heikki Krogerus Cc: Felipe Balbi , Oliver Neukum , Felipe Balbi , Mathias Nyman , Greg KH , linux-kernel@vger.kernel.org, "linux-usb@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 17, 2016 at 7:58 PM, Heikki Krogerus wrote: > On Wed, Feb 17, 2016 at 03:36:46PM +0200, Felipe Balbi wrote: >> >> Hi, >> >> Heikki Krogerus writes: >> > On Wed, Feb 17, 2016 at 11:36:52AM +0100, Oliver Neukum wrote: >> >> On Wed, 2016-02-17 at 12:29 +0200, Felipe Balbi wrote: >> >> > Hi, >> >> > >> >> > Oliver Neukum writes: >> >> > > On Wed, 2016-02-17 at 09:58 +0200, Heikki Krogerus wrote: >> >> > >> On Tue, Feb 16, 2016 at 02:39:47PM +0100, Oliver Neukum wrote: >> >> >> >> > >> > Yes, but we need an API. We can't keep adding to it. So if that >> >> > >> > is to be supported, it needs to be defined now. >> >> > >> >> >> > >> When you say API, do you mean the API the class provides to the >> >> > >> drivers? Or did you mean ABI which would be the sysfs in this case? >> >> > > >> >> > > The API to user space. That is the point. We cannot break user space. >> >> > > Once this sysfs API is upstream we are stuck with it. >> >> > >> >> > yeah, in fact I have been wondering if sysfs is the best interface to >> >> >> >> That is the discussion we must have. >> >> >> >> > userspace. I talked with Heikki a few days back about this; I was >> >> > wondering if something like what the NFC folks did with netlink would be >> >> > better here. >> >> >> >> I doubt that, because the main user is likely to be udev scripts. >> >> They can easily deal with sysfs attributes. >> > >> > IMHO for high level interface like this, sysfs is ideal because of the >> > simple fact that you only need a shell to access the files. netlink >> > would make us depend on custom software, no? >> > >> > I'm not against using netlink, but what would be the benefit from it >> > in this case? >> >> With HW we see nowadays, CC stack is hidden on some microcontroller, but >> is it too far-fetched to consider a system where this is not the case ? > > There already are several USB PD stacks out there, like also Greg > pointed out. > >> Specially when we consider things like power delivery which, I know, you >> wanted to keep it out of this interface, however we would have two >> 'stacks' competing for access to the same pins, right ? > > No. This class would be the top layer for the coming stack, where ever > it ends up coming. The class is only the interface to the user space > and nothing else. > > By saying we need to keep USB Type-C separate from USB PD I meant that > the userspace access can not be mixed somewhere in layers of the USB > PD/CC stack like it has been in the USB PD stacks I've seen so far. > They assume that we always use the software USB PD stack with USB > Type-C, which as we can see is not true when the stack is implemented > in EC or firmware or some complex USB PD controller or what ever. > However, the operations the userspace needs to do are exactly the same > in both cases. > > - data role swapping > - power role swapping (depends on USB PD) > - Alternate Modes (depends on USB PD) > > And we really should not forget that we actually also have USB Type-C > PHYs that can't do any USB PD communication over the CC pin, so USB PD > is simply not always going to be available. But the data role swapping > and also accessories are still available with them, as the do not need > USB PD. > > This was the whole point with the class. It allows the different ways > of dealing with Type-C ports to be exposed to userspace in the same > way. > >> IIRC mode and role negotiation goes via CC pins using the power delivery >> protocol. If I misunderstand anything, let me know. > > The data role swap with USB Type-C connectors is in no way tied to USB > Power Delivery. The USB Type-C spec defines that when USB PD is Its not data role swap i guess its dual role, A Data role swap is tied with USB PD, > available, DR_Swap USB PD function is used to swap the role, otherwise > emulated disconnect will do the trick. I doubt a USB host with no device capability implement DRP ?? Also emulated trick(??) is not spec requirement rt ? > > Data role swapping is a must thing to have with USB Type-C connectors I guess you are referring to Dual role (DRP) and not data role (DRD). > because of the fact that the role is selected randomly. Regardless was > USB PD supported or not. > > > Thanks, > > -- > heikki > -- > To unsubscribe from this list: send the line "unsubscribe linux-usb" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html