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

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Message-ID: <20160622095016.GB19856@kuha.fi.intel.com>
Date:	Wed, 22 Jun 2016 12:50:16 +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 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.


Thanks,

-- 
heikki