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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Message-ID: <ccfa822c-bbd7-7894-8d33-b8d25814b042@roeck-us.net>
Date:   Tue, 11 Aug 2020 17:36:15 -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 8/11/20 4:21 PM, Badhri Jagan Sridharan wrote:
> Thanks Guenter ! However I don't see a reviewed-by tag :)
> 

Confused. Did you send a v2 with the changes we discussed ?
I didn't see that.

Thanks,
Guenter

> On Tue, Aug 11, 2020 at 1:18 PM Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On 8/11/20 12:39 PM, Badhri Jagan Sridharan wrote:
>>> On Tue, Aug 11, 2020 at 11:45 AM Guenter Roeck <linux@...ck-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@...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
>>>
>>> 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;
>>>>>>>
>>>>>>
>>