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

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Date:	Wed, 22 Jun 2016 15:47:03 +0200
From:	Oliver Neukum <oneukum@...e.com>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Guenter Roeck <linux@...ck-us.net>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCHv3 1/2] usb: USB Type-C connector class

On Wed, 2016-06-22 at 14:44 +0300, Heikki Krogerus wrote:
> If our port is DRD (which would be DRP in the port controller spec),
> the supported_power_roles will list:
> 
>         device, host
> 
> And the power role, if the port is Source only, the
> supported_power_roles will list:
> 
>         source
> 
> If the port is Sink only, the supported_power_roles will list:
> 
>         sink
> 
> If our port is DRP, the supported_power_roles will list:
> 
>         source, sink
> 
> What is there that is missing? We are able to express all the types of
> "Roles Supported" that the DEVICE_CAPABILITIES define, no?

No, because these are distinct in time. Some ports are DRP so they
support

device, host

at the same time. Some ports can be switched between DFP and UFP
they then either support host or device. But you lose the information
that the ports can be switched.

	Regards
		Oliver