Message-ID: <c2d689eb-5538-6af2-614f-766521100273@roeck-us.net>
Date:   Fri, 2 Oct 2020 07:26:24 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Greg KH <gregkh@...uxfoundation.org>,
        ChiYuan Huang <u0084500@...il.com>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        cy_huang <cy_huang@...htek.com>
Subject: Re: [PATCH] usb: typec: tcpm: Fix if vbus before cc, hard_reset_count
 not reset issue

On 10/2/20 6:31 AM, Greg KH wrote:
> On Tue, Sep 15, 2020 at 11:07:18AM +0800, ChiYuan Huang wrote:
>> Hi, Guenter:
>>
>> ChiYuan Huang <u0084500@...il.com> 於 2020年9月6日 週日 下午11:22寫道：
>>>
>>> Guenter Roeck <linux@...ck-us.net> 於 2020年9月5日 週六 下午11:51寫道：
>>>>
>>>> On 9/4/20 6:24 PM, ChiYuan Huang wrote:
>>>>> Guenter Roeck <linux@...ck-us.net> 於 2020年9月5日 週六 上午3:41寫道：
>>>>>>
>>>>>> On 9/3/20 9:21 AM, ChiYuan Huang wrote:
>>>>>>> Guenter Roeck <linux@...ck-us.net> 於 2020年9月3日 週四 上午12:57寫道：
>>>>>>>>
>>>>>>>> On Wed, Sep 02, 2020 at 11:35:33PM +0800, cy_huang wrote:
>>>>>>>>> From: ChiYuan Huang <cy_huang@...htek.com>
>>>>>>>>>
>>>>>>>>> Fix: If vbus event is before cc_event trigger, hard_reset_count
>>>>>>>>> won't bt reset for some case.
>>>>>>>>>
>>>>>>>>> Signed-off-by: ChiYuan Huang <cy_huang@...htek.com>
>>>>>>>>> ---
>>>>>>>>> Below's the flow.
>>>>>>>>>
>>>>>>>>> _tcpm_pd_vbus_off() -> run_state_machine to change state to SNK_UNATTACHED
>>>>>>>>> call tcpm_snk_detach() -> tcpm_snk_detach() -> tcpm_detach()
>>>>>>>>> tcpm_port_is_disconnected() will be called.
>>>>>>>>> But port->attached is still true and port->cc1=open and port->cc2=open
>>>>>>>>>
>>>>>>>>> It cause tcpm_port_is_disconnected return false, then hard_reset_count won't be reset.
>>>>>>>>> After that, tcpm_reset_port() is called.
>>>>>>>>> port->attached become false.
>>>>>>>>>
>>>>>>>>> After that, cc now trigger cc_change event, the hard_reset_count will be kept.
>>>>>>>>> Even tcpm_detach will be called, due to port->attached is false, tcpm_detach()
>>>>>>>>> will directly return.
>>>>>>>>>
>>>>>>>>> CC_EVENT will only trigger drp toggling again.
>>>>>>>>> ---
>>>>>>>>>  drivers/usb/typec/tcpm/tcpm.c | 3 +--
>>>>>>>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
>>>>>>>>> index a48e3f90..5c73e1d 100644
>>>>>>>>> --- a/drivers/usb/typec/tcpm/tcpm.c
>>>>>>>>> +++ b/drivers/usb/typec/tcpm/tcpm.c
>>>>>>>>> @@ -2797,8 +2797,7 @@ static void tcpm_detach(struct tcpm_port *port)
>>>>>>>>>               port->tcpc->set_bist_data(port->tcpc, false);
>>>>>>>>>       }
>>>>>>>>>
>>>>>>>>> -     if (tcpm_port_is_disconnected(port))
>>>>>>>>> -             port->hard_reset_count = 0;
>>>>>>>>> +     port->hard_reset_count = 0;
>>>>>>>>>
>>>>>>>>
>>>>>>>> Doesn't that mean that the state machine will never enter
>>>>>>>> error recovery ?
>>>>>>>>
>>>>>>> I think it does't affect the error recovery.
>>>>>>> All error recovery seems to check pd_capable flag.
>>>>>>>
>>>>>>> >From my below case, it's A to C cable only. There is no USBPD contract
>>>>>>> will be estabilished.
>>>>>>>
>>>>>>> This case occurred following by the below test condition
>>>>>>> Cable -> A to C (default Rp bind to vbus) connected to PC.
>>>>>>> 1. first time plugged in the cable with PC
>>>>>>> It will make HARD_RESET_COUNT  to be equal 2
>>>>>>> 2. And then plug out. At that time HARD_RESET_COUNT is till 2.
>>>>>>> 3. next time plugged in again.
>>>>>>> Due to hard_reset_count is still 2 , after wait_cap_timeout, the state
>>>>>>> eventually changed to SNK_READY.
>>>>>>> But during the state transition, no hard_reset  be sent.
>>>>>>>
>>>>>>> Defined in the USBPD policy engine, typec transition to USBPD, all
>>>>>>> variables must be reset included hard_reset_count.
>>>>>>> So it expected SNK must send hard_reset again.
>>>>>>>
>>>>>>> The original code defined hard_reset_count must be reset only when
>>>>>>> tcpm_port_is_disconnected.
>>>>>>>
>>>>>>> It doesn't make sense that it only occurred in some scenario.
>>>>>>> If tcpm_detach is called, hard_reset count must be reset also.
>>>>>>>
>>>>>>
>>>>>> If a hard reset fails, the state machine may cycle through states
>>>>>> HARD_RESET_SEND, HARD_RESET_START, SRC_HARD_RESET_VBUS_OFF,
>>>>>> SRC_HARD_RESET_VBUS_ON back to SRC_UNATTACHED. In this state,
>>>>>> tcpm_src_detach() and with it tcpm_detach() is called. The hard
>>>>>> reset counter is incremented in HARD_RESET_SEND. If tcpm_detach()
>>>>>> resets the counter, the state machine will keep cycling through hard
>>>>>> resets without ever entering the error recovery state. I am not
>>>>>> entirely sure where the counter should be reset, but tcpm_detach()
>>>>>> seems to be the wrong place.
>>>>>
>>>>> This case you specified means locally error occurred.
>>>>
>>>> It could be a local error (with the local hardware), or with the
>>>> remote partner not accepting the reset. We only know that an error
>>>> occurred.
>>>>
>>>>> It intended to re-run the state machine from typec  to USBPD.
>>>>> >From my understanding, hard_reset_count to be reset is reasonable.
>>>>>
>>>>> The normal stare from the state transition you specified is
>>>>> HARD_RESET_SEND, HARD_RESET_START -> SRC_HARD_RESET_VBUS_OFF,
>>>>> SRC_HARD_RESET_VBUS_ON -> received VBUS_EVENT then go to SRC_STARTUP.
>>>>>
>>>> The operational word is "normal". Error recovery is expected to handle
>>>> situations which are not normal.
>>>
>>> Following by the USBPD 3.0 revision 1.2, section 8.3.3.24.1
>>> The ErrorRecovery state is  used to electronically disconnect Port
>>> Partner using the USB Type-C connector.
>>> And there's one sentence to be said "The ErrorRecovery staste shall
>>> map to USB Type-C Error Recovery state operations".
>>> I also read ErrorRecovery state in USB TYPE-C 1.3 spec.
>>> Section 4.5.2.2.2.1   ErrorRecovery state requirement listed the below text.
>>> The port shall not drive VBUS or VCONN, and shall present a
>>> high-impedance to ground (above
>>> zOPEN) on its CC1 and CC2 pins.
>>> Section 4.5.2.2.2.2 Exiting from the error recovery state
>>> I read the description. The roughly meaning is to change the state to
>>> Unattached(Src or Snk) after tErrorRecovery.
>>>
>>> Summary the above text.
>>> Reset HardResetCounter is ok in tcpm_detach.
>>> My patch is just to relax the counter reset conditions during tcpm_detach().
>>> If not, it will check tcpm_port_is_disconnected().
>>> And only two scenario, the hard reset count will be cleared to 0 at this case.
>>> 1) port not attached and cc1=open and cc2=open
>>> 2) port attached and either (polarity=cc1, cc1=open) or (polarity=cc2, cc2=open)
>>>
>>> I think this judgement is narrow in tcpm_detach case.
>>>
>>>>
>>>> I don't question the need to reset the counter. The only question
>>>> is where and when to reset it.
>>>>
>>> I re-check all tcpm code for hard reset counter about the increment and reset.
>>> They all meets USBPD spec. Only the detach case, I'm wondering why it
>>> need to add the check for tcpm_port_is_disconnected().
>>>
>> Below's the real case log.
>> [ 4848.046358] VBUS off
>> [ 4848.046384] state change SNK_READY -> SNK_UNATTACHED
>> [ 4848.050908] Setting voltage/current limit 0 mV 0 mA
>> [ 4848.050936] polarity 0
>> [ 4848.052593] Requesting mux state 0, usb-role 0, orientation 0
>> [ 4848.053222] Start toggling
>> [ 4848.086500] state change SNK_UNATTACHED -> TOGGLING
>> [ 4848.089983] CC1: 0 -> 0, CC2: 3 -> 3 [state TOGGLING, polarity 0, connected]
>> [ 4848.089993] state change TOGGLING -> SNK_ATTACH_WAIT
>> [ 4848.090031] pending state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED @ 200 ms
>> [ 4848.141162] CC1: 0 -> 0, CC2: 3 -> 0 [state SNK_ATTACH_WAIT,
>> polarity 0, disconnected]
>> [ 4848.141170] state change SNK_ATTACH_WAIT -> SNK_ATTACH_WAIT
>> [ 4848.141184] pending state change SNK_ATTACH_WAIT -> SNK_UNATTACHED @ 20 ms
>> [ 4848.163156] state change SNK_ATTACH_WAIT -> SNK_UNATTACHED [delayed 20 ms]
>> [ 4848.163162] Start toggling
>> [ 4848.216918] CC1: 0 -> 0, CC2: 0 -> 3 [state TOGGLING, polarity 0, connected]
>> [ 4848.216954] state change TOGGLING -> SNK_ATTACH_WAIT
>> [ 4848.217080] pending state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED @ 200 ms
>> [ 4848.231771] CC1: 0 -> 0, CC2: 3 -> 0 [state SNK_ATTACH_WAIT,
>> polarity 0, disconnected]
>> [ 4848.231800] state change SNK_ATTACH_WAIT -> SNK_ATTACH_WAIT
>> [ 4848.231857] pending state change SNK_ATTACH_WAIT -> SNK_UNATTACHED @ 20 ms
>> [ 4848.256022] state change SNK_ATTACH_WAIT -> SNK_UNATTACHED [delayed 20 ms]
>> [ 4848.256049] Start toggling
>> [ 4848.871148] VBUS on
>> [ 4848.885324] CC1: 0 -> 0, CC2: 0 -> 3 [state TOGGLING, polarity 0, connected]
>> [ 4848.885372] state change TOGGLING -> SNK_ATTACH_WAIT
>> [ 4848.885548] pending state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED @ 200 ms
>> [ 4849.088240] state change SNK_ATTACH_WAIT -> SNK_DEBOUNCED [delayed 200 ms]
>> [ 4849.088284] state change SNK_DEBOUNCED -> SNK_ATTACHED
>> [ 4849.088291] polarity 1
>> [ 4849.088769] Requesting mux state 1, usb-role 2, orientation 2
>> [ 4849.088895] state change SNK_ATTACHED -> SNK_STARTUP
>> [ 4849.088907] state change SNK_STARTUP -> SNK_DISCOVERY
>> [ 4849.088915] Setting voltage/current limit 5000 mV 0 mA
>> [ 4849.088927] vbus=0 charge:=1
>> [ 4849.090505] state change SNK_DISCOVERY -> SNK_WAIT_CAPABILITIES
>> [ 4849.090828] pending state change SNK_WAIT_CAPABILITIES -> SNK_READY @ 240 ms
>> [ 4849.335878] state change SNK_WAIT_CAPABILITIES -> SNK_READY [delayed 240 ms]
>>
>> You can see the next type c attach log.
>> It directly change state from SNK_WAIT_CAPABILITIES to SNK_READY due
>> to not reset hard_reset_count.
>>
>> It's easy to reproduce if you plugout USB Adapater w/i AtoC cable connected.
> 
> What ever happened with this patch, is there still disagreement?
> 

Yes, there is. I wouldn't have added the conditional without reason,
and I am concerned that removing it entirely will open another problem.
Feel free to apply, though - I can't prove that my concern is valid,
and after all we'll get reports from the field later if it is.

Guenter

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