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 11:45:07 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Badhri Jagan Sridharan <badhri@...gle.com>
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 Tue, Aug 11, 2020 at 11:24:07AM -0700, Badhri Jagan Sridharan wrote:
> 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?
> 
That, or the driver might be buggy, or the hardware does't signal a status
update, or the update gets lost. I think we should have some backup,
to trigger if the event is not received in a reasonable amout of time.
I don't know if the specification has some kind of maximum limit. If
not, we should still have something.

Thanks,
Guenter

> 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;
> > >
> >