linux-kernel - Re: [PATCH v1] usb: typec: tcpm: Fix TDA 2.2.1.1 and TDA 2.2.1.2 failures

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Date:   Tue, 11 Aug 2020 11:24:07 -0700
From:   Badhri Jagan Sridharan <badhri@...gle.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] usb: typec: tcpm: Fix TDA 2.2.1.1 and TDA 2.2.1.2 failures

On Mon, Aug 10, 2020 at 6:51 PM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 8/10/20 6:11 PM, Badhri Jagan Sridharan wrote:
> >>From the spec:
> > "7.1.5 Response to Hard Resets
> > Hard Reset Signaling indicates a communication failure has occurred and
> > the Source Shall stop driving VCONN, Shall remove Rp from the VCONN pin
> > and Shall drive VBUS to vSafe0V as shown in Figure 7-9. The USB connection
> > May reset during a Hard Reset since the VBUS voltage will be less than
> > vSafe5V for an extended period of time. After establishing the vSafe0V
> > voltage condition on VBUS, the Source Shall wait tSrcRecover before
> > re-applying VCONN and restoring VBUS to vSafe5V. A Source Shall conform
> > to the VCONN timing as specified in [USB Type-C 1.3]."
> >
> > Signed-off-by: Badhri Jagan Sridharan <badhri@...gle.com>
> > ---
> >  drivers/usb/typec/tcpm/tcpm.c | 16 +++++++++++++---
> >  1 file changed, 13 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> > index 3ef37202ee37..e41c4e5d3c71 100644
> > --- a/drivers/usb/typec/tcpm/tcpm.c
> > +++ b/drivers/usb/typec/tcpm/tcpm.c
> > @@ -3372,13 +3372,19 @@ static void run_state_machine(struct tcpm_port *port)
> >                       tcpm_set_state(port, SNK_HARD_RESET_SINK_OFF, 0);
> >               break;
> >       case SRC_HARD_RESET_VBUS_OFF:
> > -             tcpm_set_vconn(port, true);
> > +             /*
> > +              * 7.1.5 Response to Hard Resets
> > +              * Hard Reset Signaling indicates a communication failure has occurred and the
> > +              * Source Shall stop driving VCONN, Shall remove Rp from the VCONN pin and Shall
> > +              * drive VBUS to vSafe0V as shown in Figure 7-9.
> > +              */
> > +             tcpm_set_vconn(port, false);
> >               tcpm_set_vbus(port, false);
> >               tcpm_set_roles(port, port->self_powered, TYPEC_SOURCE,
> >                              tcpm_data_role_for_source(port));
> > -             tcpm_set_state(port, SRC_HARD_RESET_VBUS_ON, PD_T_SRC_RECOVER);
>
> I am a bit concerned about this. If I understand correctly, it means that
> we won't turn VBUS back on unless a SRC_HARD_RESET_VBUS_OFF PD event is received.
> Is that correct ? What happens if that event is never received ?
>
> Thanks,
> Guenter

The term PD event is a little ambiguous to me. Trying to summarize the workflow.
Lower level tcpc driver would have to call tcpm_vbus_change which
would in-turn trigger TCPM_VBUS_EVENT
and queries port->tcpc->get_vbus to get the vbus status. It is not
really a PD protocol driven event hence the
confusion.

"What happens if that event is never received ?"
Yeah TCPM would be in SRC_HARD_RESET_VBUS_OFF till the tcpc calls the
tcpm_vbus_change.
Do you suspect that existing tcpc would not have the capability to
monitor vbus status while sourcing and call tcpm_vbus_change?

Thanks,
Badhri


> >               break;
> >       case SRC_HARD_RESET_VBUS_ON:
> > +             tcpm_set_vconn(port, true);
> >               tcpm_set_vbus(port, true);
> >               port->tcpc->set_pd_rx(port->tcpc, true);
> >               tcpm_set_attached_state(port, true);
> > @@ -3944,7 +3950,11 @@ static void _tcpm_pd_vbus_off(struct tcpm_port *port)
> >               tcpm_set_state(port, SNK_HARD_RESET_WAIT_VBUS, 0);
> >               break;
> >       case SRC_HARD_RESET_VBUS_OFF:
> > -             tcpm_set_state(port, SRC_HARD_RESET_VBUS_ON, 0);
> > +             /*
> > +              * After establishing the vSafe0V voltage condition on VBUS, the Source Shall wait
> > +              * tSrcRecover before re-applying VCONN and restoring VBUS to vSafe5V.
> > +              */
> > +             tcpm_set_state(port, SRC_HARD_RESET_VBUS_ON, PD_T_SRC_RECOVER);
> >               break;
> >       case HARD_RESET_SEND:
> >               break;
> >
>