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Subject: Re: [PATCH v1] usb: typec: tcpm: Fix TDA 2.2.1.1 and TDA 2.2.1.2
 failures
To:     Badhri Jagan Sridharan <badhri@google.com>
Cc:     Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        USB <linux-usb@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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From:   Guenter Roeck <linux@roeck-us.net>
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Date:   Tue, 11 Aug 2020 13:18:03 -0700
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On 8/11/20 12:39 PM, Badhri Jagan Sridharan wrote:
> On Tue, Aug 11, 2020 at 11:45 AM Guenter Roeck <linux@roeck-us.net> wrote:
>>
>> 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@roeck-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@google.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
> 
> Got it ! The specification actually has a bound for vbus off.
> tSafe0V  - Time to reach vSafe0V max - 650ms. (PD_T_SAFE_0V).
> So I will bound it to that.
> 

Excellent. Thanks a lot for looking into this!

Guenter

>>From Table 7-12 Sequence Description for a Source Initiated Hard Reset:
> 4.Policy Engine waits tPSHardReset after sending Hard Reset Signaling
> and then tells the Device Policy Manager to instruct the power supply
> to perform a Hard Reset. The transition to vSafe0V Shall occur within
> tSafe0V (t2).
> 5 After tSrcRecover the Source applies power to VBUS in an attempt to
> re-establish communication with the Sink and resume USB Default
> Operation. The transition to vSafe5V Shall occur within tSrcTurnOn
> (t4).
> 
> Thanks,
> Badhri
> 
>>
>>> 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;
>>>>>
>>>>