On Thu, May 18, 2017 at 11:13:51AM +0200, Oliver Neukum wrote: > 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. > Not really sure I can follow. If a partner does not support PD, there is no real distinction between data role and power role, or am I missing something ? Are you saying that, if a partner does not support PD, user space should request a data role swap instead, and that this would be acceptable for you ? I don't really understand the difference - a data role swap doesn't cause a disconnect either if the partner supports PD, and it would still result in a disconnect/reconnect sequence if the partner does not support PD - but if it works for you, fine with me. Badhri, would that work for us ? Thanks, Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
