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Subject: Re: [PATCH v2] usb: typec: tcpm: collision avoidance
To:     Kyle Tso <kyletso@google.com>,
        Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Cc:     Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Greg KH <gregkh@linuxfoundation.org>,
        Badhri Jagan Sridharan <badhri@google.com>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20190322121745.159768-1-kyletso@google.com>
 <20190404141345.GF21319@kuha.fi.intel.com>
 <08a6d422-e8f7-303e-7bf1-952344f2c182@roeck-us.net>
 <CAGZ6i=2zKLhS4By8Xanc863G+jSxPYg8SLU-UHkY94r5MiEYag@mail.gmail.com>
 <20190409130230.GC20058@kuha.fi.intel.com>
 <20190409130649.GD20058@kuha.fi.intel.com>
 <9c9d17e3-bd99-c877-359c-a0a1b10a8d73@redhat.com>
 <AM5PR1001MB099440C3AA6DA6BA2AB0F2AE802E0@AM5PR1001MB0994.EURPRD10.PROD.OUTLOOK.COM>
 <CAGZ6i=0rRgNH5bU-zcP58MNi+VSa+xeAQWL67egaZ-ui-ebmYA@mail.gmail.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <9f9a2de9-2cfb-385c-8e99-54b2587113ce@redhat.com>
Date:   Wed, 10 Apr 2019 17:45:12 +0200
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Hi Kyle,

On 10-04-19 14:49, Kyle Tso wrote:
> On Wed, Apr 10, 2019 at 6:32 PM Adam Thomson
> <Adam.Thomson.Opensource@diasemi.com> wrote:
>>
>> On 09 April 2019 15:41, Hans de Goede wrote:
>>
>>> Hi,
>>>
>>> On 09-04-19 15:06, Heikki Krogerus wrote:
>>>> On Tue, Apr 09, 2019 at 04:02:30PM +0300, Heikki Krogerus wrote:
>>>>> +Hans
>>>>>
>>>>> On Mon, Apr 08, 2019 at 10:17:35PM +0800, Kyle Tso wrote:
>>>>>> On Fri, Apr 5, 2019 at 9:42 PM Guenter Roeck <linux@roeck-us.net> wrote:
>>>>>>>
>>>>>>> On 4/4/19 7:13 AM, Heikki Krogerus wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> On Fri, Mar 22, 2019 at 08:17:45PM +0800, Kyle Tso wrote:
>>>>>>>>> This patch provides the implementation of Collision Avoidance
>>>>>>>>> introduced in PD3.0. The start of each Atomic Message Sequence
>>>>>>>>> (AMS) initiated by the port will be denied if the current AMS is
>>>>>>>>> not interruptible. The Source port will set the CC to SinkTxNG if
>>>>>>>>> it is going to initiate an AMS, and SinkTxOk otherwise.
>>>>>>>>> Meanwhile, any AMS initiated by a Sink port will be denied in
>>>>>>>>> TCPM if the port partner (Source) sets SinkTxNG except for HARD_RESET
>>> and SOFT_RESET.
>>>>>>>>
>>>>>>>> I tested this with my GDBWin which has fusb302. When I plug-in
>>>>>>>> DisplayPort adapter, the partner device never gets registered, and
>>>>>>>> I see steady flow of warnings from fusb302:
>>>>>>>>
>>>>>>>
>>>>>>> FWIW, I made multiple attempts to review the patch. Each time I get
>>>>>>> stuck after a while and notice that I don't understand what is going on.
>>>>>>>
>>>>>>> Maybe the state machine needs a complete overhaul. It seems to have
>>>>>>> reached a point where it is getting too complex to understand what is going
>>> on.
>>>>>>>
>>>>>>>> [  693.391176] Vconn is on during toggle start [  693.391250]
>>>>>>>> WARNING: CPU: 2 PID: 30 at drivers/usb/typec/tcpm/fusb302.c:562
>>>>>>>> fusb302_set_toggling+0x129/0x130 [fusb302] [  693.400293] Modules
>>> linked in: intel_xhci_usb_role_switch fusb302 tcpm roles pi3usb30532 i915 typec
>>> intel_gtt intel_cht_int33fe
>>>>>>>> [  693.406309] CPU: 2 PID: 30 Comm: kworker/u8:1 Tainted: G        W
>>> 5.1.0-rc3-heikki+ #17
>>>>>>>> [  693.408434] cht_wcove_pwrsrc cht_wcove_pwrsrc: Could not detect
>>>>>>>> charger type [  693.412278] Hardware name: Default string Default
>>>>>>>> string/Default string, BIOS 5.11 05/25/2017 [  693.412283]
>>>>>>>> Workqueue: i2c-fusb302 tcpm_state_machine_work [tcpm] [
>>>>>>>> 693.424256] RIP: 0010:fusb302_set_toggling+0x129/0x130 [fusb302] [
>>>>>>>> 693.427234] Code: 89 df e8 da ef ff ff 85 c0 78 c6 c6 83 b0 01 00
>>>>>>>> 00 00 eb b7 b9 02 00 00 00 e9 48 ff ff ff 48 c7 c7 20 e8 21 a0 e8
>>>>>>>> 8e 0c e4 e0 <0f> 0b e9 58 ff ff ff 41 55 4c 8d 6f e8 41 54 41 89
>>>>>>>> f4 55 53 48 8d [  693.436204] RSP: 0000:ffffc9000076bd90 EFLAGS:
>>>>>>>> 00010286 [  693.439174] RAX: 0000000000000000 RBX:
>>>>>>>> ffff888178080028 RCX: 0000000000000000 [  693.442157] RDX:
>>>>>>>> 000000000000001f RSI: ffffffff8259051f RDI: ffffffff8259091f [
>>>>>>>> 693.445130] RBP: 0000000000000003 R08: ffffffff82590500 R09:
>>>>>>>> 00000000000202c0 [  693.448100] R10: 0000010cb24a3d18 R11:
>>>>>>>> 000000000000001e R12: ffff8881780801b0 [  693.451086] R13:
>>> ffffffffa021e4e5 R14: 0000000000000003 R15: ffff888178080040 [  693.454060] FS:
>>> 0000000000000000(0000) GS:ffff88817bb00000(0000) knlGS:0000000000000000 [
>>> 693.460009] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [  693.462984] CR2:
>>> 00000000f7fb74a0 CR3: 000000000200d000 CR4: 00000000001006e0 [  693.465969]
>>> Call Trace:
>>>>>>>> [  693.468937]  tcpm_set_cc+0xb9/0x170 [fusb302] [  693.471894]
>>>>>>>> tcpm_ams_start+0x1b8/0x2a0 [tcpm]
>>>>>>>
>>>>>>> tcpm_ams_start() sets TYPEC_CC_RP_1_5 unconditionally, no matter
>>>>>>> what. This causes the fusb302 code to start toggling. As such, it
>>>>>>> may well attempt to start toggling in the wrong state.
>>>>>>>
>>>>>>> Guenter
>>>>>>>
>>>>>>
>>>>>> I read the fusb302 spec but failed to find the statement that says
>>>>>> it should "set toggling" when CC switches among default/medium/high.
>>>>>>
>>>>>> quot from fusb302 spec:
>>>>>> "The FUSB302 allows the host software to change the charging current
>>>>>> capabilities of the port through the HOST_CUR control bits. If the
>>>>>> HOST_CUR bits are changed prior to attach, the FUSB302 automatically
>>>>>> indicates the programmed current capability when a device is attached.
>>>>>> If the current capabilities are changed after a device is attached,
>>>>>> the FUSB302 immediately changes the CC line to the programmed
>>>>>> capability."
>>>>>>
>>>>>> Is it possible to skip fusb302_set_toggling() @ line#658 if
>>>>>> tcpm_set_cc() is called in order to switch the cc among
>>>>>> default/medium/high of Rp ?
>>>>
>>>> Hans, you introduced that in commit daf81d0137a9c ("usb: typec:
>>>> fusb302: Refactor / simplify tcpm_set_cc()"), so could you take a look
>>>> at this.
>>>
>>> I do not believe that that commit introduces the fusb302_set_toggling() as the
>>> subject of the commit says it just refactors things, the set_toggling call was
>>> introduced by:
>>>
>>> commit ea3b4d5523bc8("usb: typec: fusb302: Resolve fixed power role contract
>>> setup")
>>>
>>> Before that:
>>>
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/u
>>> sb/typec/tcpm/fusb302.c?id=40326e857c57a0095d3f9d72c14cb13aef4ca564
>>>
>>> tcpm_set_cc actually turned toggling off in all cases.
>>>
>>> I've no doubt that Adam was seeing a real problem, but I've doubted if this was
>>> the right fix before. I even had it reverted in my tree for a while, but since in my
>>> use-cases so far it has not caused any problems I've not looked into it further.
>>
>>  From my recollection, that was the only way to generate the necessary event from
>> fusb302 to indicate a connection, when the device was in a fixed role state
>> (i.e. only source or only sink). Without it the driver doesn't work in these
>> scenarios as there's no TOGDONE event generated by fusb302, so no eventual call
>> to 'tcpm_cc_change()' to tell TCPM that something has happened and move on the
>> state machine. Not all devices will be DRP so we have to account for this.
>>
> 
> The switch among different Rp values on CC pins comes from TCPM and
> after the switch finishes, TCPM doesn't need to update the CC status because
> this kind of switch won't affect the state machine.
> 
>>>
>>> In the mean time the code has changed quite a bit though, so making
>>> tcpm_set_cc() behave as it did before, see:
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/u
>>> sb/typec/tcpm/fusb302.c?id=40326e857c57a0095d3f9d72c14cb13aef4ca564
>>>
>>> Will require writing something from scratch based on the new code which
>>> mimicks the behaviour of the old code; and then we also need to fix Adam's
>>> problem on top.
>>>
>>> Regards,
>>>
>>> Hans
> 
> I tried to fix this with below changes and it works.
> 
> ============================================
> --- a/drivers/usb/typec/tcpm/fusb302.c
> +++ b/drivers/usb/typec/tcpm/fusb302.c
> @@ -110,6 +110,9 @@ struct fusb302_chip {
>          enum typec_cc_status cc2;
>          u32 snk_pdo[PDO_MAX_OBJECTS];
> 
> +       /* Local pin status */
> +       enum typec_cc_status cc;
> +
>   #ifdef CONFIG_DEBUG_FS
>          struct dentry *dentry;
>          /* lock for log buffer access */
> @@ -611,6 +614,19 @@ static int tcpm_set_cc(struct tcpc_dev *dev, enum
> typec_cc_status cc)
>          enum toggling_mode mode;
> 
>          mutex_lock(&chip->lock);
> +       if ((chip->cc == TYPEC_CC_RP_DEF || chip->cc == TYPEC_CC_RP_1_5 ||
> +            chip->cc == TYPEC_CC_RP_3_0) && (cc == TYPEC_CC_RP_DEF ||
> +            cc == TYPEC_CC_RP_1_5 || cc == TYPEC_CC_RP_3_0)) {
> +               ret = fusb302_set_src_current(chip, cc_src_current[cc]);
> +               if (ret < 0) {
> +                       fusb302_log(chip, "cannot set src current %s, ret=%d\n",
> +                                   typec_cc_status_name[cc], ret);
> +                       goto done;
> +               }
> +               fusb302_log(chip, "cc := %s", typec_cc_status_name[cc]);
> +               goto rp_switch;
> +       }
> +
>          switch (cc) {
>          case TYPEC_CC_OPEN:
>                  mode = TOGGLING_MODE_OFF;
> @@ -659,6 +675,8 @@ static int tcpm_set_cc(struct tcpc_dev *dev, enum
> typec_cc_status cc)
>          if (ret < 0)
>                  fusb302_log(chip, "cannot set toggling mode, ret=%d", ret);
> 
> +rp_switch:
> +       chip->cc = cc;
>   done:
>          mutex_unlock(&chip->lock);


I understand what you are trying to do here and I agree that just
changing the Cc pins this way should not start toggling. But I
would rather go back to the functionality of tcpm_set_cc() from
before commit ea3b4d5523bc8("usb: typec: fusb302: Resolve fixed power role contract setup")

Starting toggling from tcpm_set_cc() just feels wrong; and currently
power role swapping is broken with the fusb302, which IIRC used to
work. I suspect this is related.

I plan to write a patch tomorrow to functionally take tcpm_set_cc()
back to the way it was before. This should fix your case and
I hope this also fixes power-role swapping.

This will re-introduce Adam Thomson's problem, but I have a feeling
that that actually needs a fix in the tcpm.c code rather then at
the fusb302 level.

Anyways first let me attempt to write the promised patch and then
we will see from there.

Regards,

Hans


> ============================================
> 
> TCPM logs:
> 
> [   52.267343] CC1: 0 -> 1, CC2: 0 -> 2 [state DRP_TOGGLING, polarity
> 0, connected]
> [   52.267354] state change DRP_TOGGLING -> SRC_ATTACH_WAIT
> [   52.267435] pending state change SRC_ATTACH_WAIT -> SNK_TRY @ 200 ms
> [   52.466852] state change SRC_ATTACH_WAIT -> SNK_TRY [delayed 200 ms]
> [   52.466876] cc:=2
> [   52.471851] pending state change SNK_TRY -> SNK_TRY_WAIT @ 140 ms
> [   52.610244] state change SNK_TRY -> SNK_TRY_WAIT [delayed 140 ms]
> [   52.610256] state change SNK_TRY_WAIT -> SRC_TRYWAIT
> [   52.610298] cc:=3
> [   52.613262] pending state change SRC_TRYWAIT ->
> SRC_TRYWAIT_UNATTACHED @ 140 ms
> [   52.625248] CC1: 1 -> 1, CC2: 2 -> 2 [state SRC_TRYWAIT, polarity
> 0, connected]
> [   52.625261] state change SRC_TRYWAIT -> SRC_TRYWAIT_DEBOUNCE
> [   52.625299] pending state change SRC_TRYWAIT_DEBOUNCE ->
> SRC_ATTACHED @ 200 ms
> [   52.823417] state change SRC_TRYWAIT_DEBOUNCE -> SRC_ATTACHED
> [delayed 200 ms]
> [   52.823425] polarity 1
> [   52.823458] Requesting mux state 1, usb-role 1, orientation 2
> [   52.846919] vconn:=1
> [   52.854536] vbus:=1 charge=0
> [   52.893437] pending state change SRC_ATTACHED -> SRC_UNATTACHED @ 480 ms
> [   52.894715] VBUS on
> [   52.894718] state change SRC_ATTACHED -> SRC_STARTUP
> [   52.894733] AMS POWER_NEGOTIATION start
> [   52.894736] cc:=4
> [   52.895043] state change SRC_STARTUP -> AMS_START in AMS POWER_NEGOTIATION
> [   52.895046] state change AMS_START -> SRC_SEND_CAPABILITIES in AMS
> POWER_NEGOTIATION
> [   52.895048] PD TX, header: 0x11a1
> [   52.910309] PD TX complete, status: 0
> [   52.910346] pending state change SRC_SEND_CAPABILITIES ->
> HARD_RESET_SEND @ 150 ms in AMS POWER_NEGOTIATION
> [   52.912383] PD RX, header: 0x1042 [1]
> [   52.912387] state change SRC_SEND_CAPABILITIES -> SRC_NEGOTIATE_CAPABILITIES
> [   52.912398] Requested 5000 mV, 900 mA for 900 / 900 mA
> [   52.912400] PD TX, header: 0x363
> [   52.915725] PD TX complete, status: 0
> [   52.915765] pending state change SRC_NEGOTIATE_CAPABILITIES ->
> SRC_TRANSITION_SUPPLY @ 35 ms
> [   52.950125] state change SRC_NEGOTIATE_CAPABILITIES ->
> SRC_TRANSITION_SUPPLY [delayed 35 ms]
> [   52.950139] PD TX, header: 0x566
> [   52.953910] PD TX complete, status: 0
> [   52.955573] state change SRC_TRANSITION_SUPPLY -> SRC_READY
> [   52.957359] PD TX, header: 0x176f
> [   52.962785] PD TX complete, status: 0
> [   52.966026] PD RX, header: 0x524f [1]
> [   52.966037] Rx VDM cmd 0xff008041 type 1 cmd 1 len 5
> [   52.966081] Identity: 04b4:1120.0000
> [   52.966106] PD TX, header: 0x196f
> [   52.969875] PD TX complete, status: 0
> [   52.972298] PD RX, header: 0x244f [1]
> [   52.972304] Rx VDM cmd 0xff008042 type 1 cmd 2 len 2
> [   52.972308] SVID 1: 0xff01
> [   52.972340] PD TX, header: 0x1b6f
> [   52.976066] PD TX complete, status: 0
> [   52.986511] PD RX, header: 0x264f [1]
> [   52.986516] Rx VDM cmd 0xff018043 type 1 cmd 3 len 2
> [   52.986520]  Alternate mode 0: SVID 0xff01, VDO 1: 0x00000405
>