On Thu, Jul 10, 2025, John Keeping wrote:

When the phy is acting as a Type C mux, it may need to reset when the
cable direction changes.  But this should not happen while DWC3 is
trying to use the USB connection.

In this case, there must be a connection manager to notify the phy of
the orientation change and tcpm_mux_set() ensures this happens before
DWC3's role switch is informed of a change.

It should not be possible to go directly from device->device or
host->host with a change in orientation without transitioning through
the "none" role as the cable is unplugged.  So ensuring that DWC3 always

The controller is either host or device mode. It's odd to use "none" to
indicate connection.

informs the phy of the new mode whenever a plug is detected should be
sufficient for the phy to safely reset itself at a time that is safe for
DWC3.

Couldn't the phy do this as it detects connection/disconnection.

It seems what you need is a full controller initialization upon new
connection on orientation change, and you're using role_switch selecting
"none" to do so.

I'm not sure if role-switch has the right interface to do so. Perhaps we
can introduce one? I don't think we should change the behavior of the
current flow and apply that to all other platforms.

Thanks,
Thinh

Lifting the special-case for desired_dr_mode==0 in __dwc3_set_mode() is
sufficient to allow using the unset mode for USB_ROLE_NONE.  The
handling already disables the old mode and then simply does not enable a
new one.

If an external device is notifying USB role switches, then it is not
necessary to set the default role when USB_ROLE_NONE is passed.