On Wed, Jun 22, 2016 at 12:14:55PM +0200, Oliver Neukum wrote:
> On Wed, 2016-06-22 at 12:50 +0300, Heikki Krogerus wrote:
> > On Tue, Jun 21, 2016 at 10:25:05PM +0200, Oliver Neukum wrote:
> > > On Tue, 2016-06-21 at 17:51 +0300, Heikki Krogerus wrote:
> > > > +What: /sys/class/typec/<port>/supported_data_roles
> > > > +Data: June 2016
> > > > +Contact: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
> > > > +Description:
> > > > + Lists the USB data roles, host or device, the port is
> > > > capable
> > > > + of supporting.
> > >
> > > On third thought, this is a problem. Looking at 4.4.8.1
> > > DEVICE_CAPABILITIES (Required) of USB Type-C Port Controller
> > > Interface Specification we lack capability.
> > >
> > > A port that can do DRP is not the same thing as a port that
> > > can be switched between DFP and UFP. We cannot express that.
> >
> > What do you mean? DRP means we support and are able to swap the data
>
> No. That is the error. We support them concurrently. And that is not
> obvious. It is perfectly possible to support both but not concurrently.
>
> > role, but it just does not mean we can act as both source and sink. And
> > that information we already get from separate attribute:
> > "supported_power_roles".
>
> But it is different. Suppose we have a port that can be switched between
> UFP and DFP, as the spec defines. If it is switched to DFP and we plug
> in a DFP it will not work. UFP into UFP has the same result.
>
> Plugging it into a DRP will always work.
>
> It is true that both support host and device, but the capability of
> the ports is different. And that is not expressed.
Sorry but I don't think I understand?
So if we can act only as UFP, the supported_data_roles will list:
device
If we can act only as DFP, the supported_data_roles will list:
host
If our port is DRD (which would be DRP in the port controller spec),
the supported_power_roles will list:
device, host
And the power role, if the port is Source only, the
supported_power_roles will list:
source
If the port is Sink only, the supported_power_roles will list:
sink
If our port is DRP, the supported_power_roles will list:
source, sink
What is there that is missing? We are able to express all the types of
"Roles Supported" that the DEVICE_CAPABILITIES define, no?
Thanks,
--
heikki
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