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. > > 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
