linux-kernel - Re: [RFC PATCHv2] usb: USB Type-C Connector Class

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Message-ID: <20160520112402.GC12663@kuha.fi.intel.com>
Date:	Fri, 20 May 2016 14:24:02 +0300
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Oliver Neukum <oneukum@...e.com>
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Rajaram R <rajaram.officemail@...il.com>,
	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [RFC PATCHv2] usb: USB Type-C Connector Class

On Thu, May 19, 2016 at 04:47:17PM +0200, Oliver Neukum wrote:
> On Thu, 2016-05-19 at 15:44 +0300, Heikki Krogerus wrote:
> > The purpose of this class is to provide unified interface for user
> > space to get the status and basic information about USB Type-C
> > Connectors in the system, control data role swapping, and when USB PD
> > is available, also power role swapping and Alternate Modes.
> > 
> > Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > ---
> >  drivers/usb/Kconfig         |   2 +
> >  drivers/usb/Makefile        |   2 +
> >  drivers/usb/type-c/Kconfig  |   7 +
> >  drivers/usb/type-c/Makefile |   1 +
> >  drivers/usb/type-c/typec.c  | 957 ++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/usb/typec.h   | 230 +++++++++++
> >  6 files changed, 1199 insertions(+)
> >  create mode 100644 drivers/usb/type-c/Kconfig
> >  create mode 100644 drivers/usb/type-c/Makefile
> >  create mode 100644 drivers/usb/type-c/typec.c
> >  create mode 100644 include/linux/usb/typec.h
> > 
> > Hi,
> > 
> > Like I've told some of you guys, I'm trying to implement a bus for
> > the Alternate Modes, but I'm still nowhere near finished with that
> > one, so let's just get the class ready now. The altmode bus should in
> > any case not affect the userspace interface proposed in this patch.
> > 
> > As you can see, the Alternate Modes are handled completely differently
> > compared to the original proposal. Every Alternate Mode will have
> > their own device instance (which will be then later bound to an
> > Alternate Mode specific driver once we have the bus), but also every
> > partner, cable and cable plug will have their own device instances
> > representing them.
> 
> That raises a question. If I read the standard correctly, alternate
> modes could be combinable. So how do you represent that.
> 
> > An other change is that the data role is now handled in two ways.
> > The current_data_role file will represent static mode of the port, and
> > it will use the names for the roles as they are defined in the spec:
> > DFP, UFP and DRP. This file should be used if the port needs to be
> > fixed to one specific role with DRP ports. So this approach will
> > replace the suggestions for "preferred" data role we had. The
> > current_usb_data_role will use values "host" and "device" and it will
> > be used for data role swapping when already connected.
> 
> Please explain. How does that express DRP but prefered master?

Sorry but I'm not sure what you mean here. If the port is capable of
being used as dual role port (DRP in the supported_data_roles file),
that is the only case where you can select the role with this file. So
I would imagine that in your case you want to make the port act as
DFP only, right? But if the port is capable of acting only as UFP, you
are stuck with that role.

> > I Hope I remembered to CC everybody interested.
> 
> Alternate modes can be left involuntarily. So we need a method of
> notification.

Yes, that is missing indeed.


Thanks,

-- 
heikki