On Wed, Jun 01, 2016 at 04:29:26PM -0700, Guenter Roeck wrote: > On Wed, Jun 01, 2016 at 11:26:09AM +0200, Oliver Neukum wrote: > > On Thu, 2016-05-19 at 15:44 +0300, Heikki Krogerus wrote: > > > Just noticed that the "active" file is for now read only, but it needs > > > to be changed to writable. That file will of course provide means for > > > the userspace to Exit and Enter modes. But please note that the > > > responsibility of the dependencies between the modes, say, if a plug > > > needs to be in one mode or the other in order for the partner to enter > > > some specific mode, will fall on the Alternate Mode specific drivers > > > once we have the altmode bus. I remember there were concerns about > > > this in the original thread. > > > > There's one thing we haven't touched upon yet. And I cannot really find > > an answer in the spec. > > > > What do we do if we return from S4 or S3? I think we need to restore > > the ALternate Mode because our display may be running over that > > Alternate Mode. > > If we want to support USB persist we also need to restore data role > > after S4. > > > I don't have an answer ... but another interesting question. > > How do we distinguish between alternate modes supported by a host vs. > alternate modes supported by a sink ? typec_capability includes a pointer > to alternate modes supportedf by the connector, but it is not clear if > those are alternate modes supported as host, or alternate modes supported > as device, or alternate modes supported by both. > > This doesn't matter much if only a fixed role is supported, but it does matter > for dual role ports. A laptop will typically only support DisplayPort as host, > for example.
The DP alternate mode spec actually separates the display role from Type-C role. A laptop most likely would only support the modes for display host roles, but if the port was DRP port then it would still do so in both Type-C roles. So basically, even if the display was Type-C host, it would still work as a display when attached to the laptop. > Any idea ? I'm actually not sure this is a problem. Thanks, -- heikki
