linux-kernel - Re: [PATCH v2] usb: typec: tcpm: collision avoidance

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Message-ID: <7dd7ce29-b4e5-02c1-6bdc-11d0e1f77a5f@redhat.com>
Date:   Wed, 10 Apr 2019 18:49:08 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        Kyle Tso <kyletso@...gle.com>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Greg KH <gregkh@...uxfoundation.org>,
        Badhri Jagan Sridharan <badhri@...gle.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: typec: tcpm: collision avoidance


> 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.