Re: [PATCH] usb: typec: Defer checking of valid power role swap to low level drivers

From: Guenter Roeck
Date: Wed May 17 2017 - 05:36:53 EST

On 05/17/2017 12:34 AM, Oliver Neukum wrote:
Am Mittwoch, den 17.05.2017, 00:32 -0700 schrieb Badhri Jagan


"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.