Re: [PATCH v2] usb: typec: tcpm: collision avoidance

From: Hans de Goede
Date: Wed Apr 10 2019 - 12:49:14 EST



If I understand the datasheet correctly:

"The FUSB302 has the capability to do autonomous
DRP toggle. In autonomous toggle the FUSB302
internally controls the PDWN1, PDWN2, PU_EN1 and
PU_EN2, MEAS_CC1 and MEAS_CC2 and implements
a fixed DRP toggle between presenting as a SRC and
presenting as a SNK. Alternately, it can present as a
SRC or SNK only and poll CC1 and CC2 continuously."

It is still attaching Rp resp Rd to CC1 or CC2 one at a time
to detect polarity, so it is still toggling, it just is not
doing dual-role toggling. This is also expected behavior for
a sink, a sink may not present Rd on both CC pins at the
same time, otherwise the source cannot detect the polarity
and the source also cannot detect if Vconn is necessary.

Erm the "a sink may not present Rd on both CC pins at the same time"
bit obviously is wrong, ignore that please.