Not Sure whether my previous response was sent properly. So re-sending. On Thu, May 18, 2017 at 2:08 PM, Badhri Jagan Sridharan <badhri@xxxxxxxxxx> wrote: > On Thu, May 18, 2017 at 9:51 AM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote: >> 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 ? Yes Geunter that should work as well. Requesting non-pd role swap either through current_power_role or current_data_role is virtually the same. > > Yes Geunter that should work as well. Requesting non-pd role swap either through > current_power_role or current_data_role is virtually the same. > >> >> 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
