Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers

[Oliver Neukum]

Am Mittwoch, den 17.05.2017, 02:36 -0700 schrieb Guenter Roeck:
> On 05/17/2017 12:34 AM, Oliver Neukum wrote:
> > 
> > Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan
> > Sridharan:
> > 
> > Hi,
> > 
> > > 
> > > "Two independent set of mechanisms are defined to allow a USB Type-C
> > > DRP to functionally swap power and data roles. When USB PD is
> > > supported, power and data role swapping is performed as a subsequent
> > > step following the initial connection process. For non-PD implementations,
> > > power/data role swapping can optionally be dealt with as part of the initial
> > > connection process."
> > 
> > Well, as I read it, without PD once a connection is established, you
> > are stuck with your role. So it seems to me that blocking a later
> > attempt to change it makes sense.
> > 
> 
> That seems to be a harsh and not very user friendly reading of the specification.
> 
> I would argue that the user doesn't care if the partner supports PD or not
> when selecting a role, and I would prefer to provide an implementation which is
> as user friendly as possible.

Data role, no question, you are right.
Power role is a different question. A switch of power role with PD should
not lead to a disconnect. Any other method might. So equating them does
not look like a good idea.

	Regards
		Oliver