linux-kernel - Re: [PATCHv3 1/2] usb: USB Type-C connector class

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Date:	Wed, 22 Jun 2016 13:03:16 +0300
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Oliver Neukum <oneukum@...e.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Guenter Roeck <linux@...ck-us.net>,
	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCHv3 1/2] usb: USB Type-C connector class

On Wed, Jun 22, 2016 at 12:50:16PM +0300, Heikki Krogerus wrote:
> On Tue, Jun 21, 2016 at 10:25:05PM +0200, Oliver Neukum wrote:
> > On Tue, 2016-06-21 at 17:51 +0300, Heikki Krogerus wrote:
> > > +What:          /sys/class/typec/<port>/supported_data_roles
> > > +Data:          June 2016
> > > +Contact:       Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > > +Description:
> > > +               Lists the USB data roles, host or device, the port is
> > > capable
> > > +               of supporting.
> > 
> > On third thought, this is a problem. Looking at 4.4.8.1
> > DEVICE_CAPABILITIES (Required) of USB Type-C Port Controller
> > Interface Specification we lack capability.
> > 
> > A port that can do DRP is not the same thing as a port that
> > can be switched between DFP and UFP. We cannot express that.
> 
> What do you mean? DRP means we support and are able to swap the data
> role, but it just does not mean we can act as both source and sink. And
> that information we already get from separate attribute:
> "supported_power_roles".
> 
> But if the port is DRP, we will always be able to swap the data role
> between DFP and UFP.

Just to clarify: DRP as it's defined in Type-C spec < 1.2 means the
data role, not power role. And that is what Universal Serial Bus
Type-CTM Port Controller specification is based on. Please correct me
if I'm wrong.


Thanks,

-- 
heikki