Re: [RFC PATCH v2 1/3] usb: dwc3: Flush pending SETUP data during stop active xfers

Thinh Nguyen
2022-03-25T01:52:23Z

Wesley Cheng wrote:
> Hi Thinh,
>
> On 3/23/2022 5:39 PM, Thinh Nguyen wrote:
>> Hi Wesley,
>>
>> Wesley Cheng wrote:
>>> Hi Thinh,
>>>
>>> On 3/22/2022 6:31 PM, Thinh Nguyen wrote:
>>>> Hi Wesley,
>>>>
>>>> Wesley Cheng wrote:
>>>>> Hi Thinh,
>>>>>
>>>>> On 2/15/2022 4:08 PM, Wesley Cheng wrote:
>>>>>> While running the pullup disable sequence, if there are pending SETUP
>>>>>> transfers stored in the controller, then the ENDTRANSFER commands on non
>>>>>> control eps will fail w/ ETIMEDOUT. As a suggestion from SNPS, in order
>>>>>> to drain potentially cached SETUP packets, SW needs to issue a
>>>>>> STARTTRANSFER command. After issuing the STARTTRANSFER, and retrying the
>>>>>> ENDTRANSFER, the command should succeed. Else, if the endpoints are not
>>>>>> properly stopped, the controller halt sequence will fail as well.
>>>>>>
>>>>>> One limitation is that the current logic will drop the SETUP data
>>>>>> being received (ie dropping the SETUP packet), however, it should be
>>>>>> acceptable in the pullup disable case, as the device is eventually
>>>>>> going to disconnect from the host.
>>>>>>
>>>>>> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
>>>>>> ---
>>>>> Just wondering if you had any inputs for this particular change? I
>>>>> think on the dequeue path discussion you had some concerns with parts of
>>>>> this change? I think the difficult part for the pullup disable path is
>>>>> that we have this API running w/ interrupts disabled, so the EP0 state
>>>>> won't be able to advance compared to the dequeue case.
>>>>
>>>> This doesn't sound right. The pullup disable (or device initiated
>>>> disconnect) should wait for the EP0 state to be EP0_SETUP_PHASE before
>>>> proceeding, which it does.
>>>>
>>> That is correct, but even though that check is passed, it doesn't
>>> prevent the host from sending another SETUP token between the pending
>>> setup packet check and run/stop clear.
>>>
>>
>> That should be fine, because we would have the TRB ready for that SETUP
>> packet.
>>
> I agree, its valid for the controller to be able to receive the next
> setup packet.
>
>>>>>
>>>>> Ideally, if there is a way to ensure that we avoid reading further setup
>>>>> packets, that would be nice, but from our discussions with Synopsys,
>>>>> this was not possible. (controller is always armed and ready to ACK
>>>>> setup tokens)
>>>>>
>>>>> I did evaluate keeping IRQs enabled and periodically releasing/attaining
>>>>> the lock between the stop active xfer calls, but that opened another can
>>>>> of worms. If you think this is the approach we should take, I can take
>>>>> a look at this implementation further.
>>>>>
>>>>
>>>> This patch doesn't look right to me. The change I suggested before
>>>> should address this (I believe Greg already picked it up). What other
>>>> problem do you see, I'm not clear what's the problem here. One potential
>>>> problem that I can see is that currently dwc3 driver doesn't wait for
>>>> active endpoints to complete/end before clearing the run_stop bit on
>>>> device initiated disconnect, but I'm not sure if that's what you're seeing.
>>>>
>>>> Please help clarify further. If there's trace points log, that'd help.
>>>>
>>> Main difference between the issue Greg recently pulled in and this one
>>> is that this is on the pullup disable patch (no dequeue involved). In
>>> this situation we will also stop active transfers, so that the
>>> controller can halt properly.
>>>
>>> I attached a few files, and will give a summary of them below:
>>> 1. pullup_disable_timeout.txt - ftrace of an instance of when we see
>>> several endxfer timeouts. Refer to line#2016.
>>>
>>> 2. lecroy+ftrace_snip.png - picture showing a matching bus sniffer log
>>> and a ftrace collected (difference instance to #1)
>>>
>>> #2 will show that we completed a SETUP transfer before entering into
>>> dwc3_gadget_stop_active_transfers(). In here, we then see DWC ACK
>>> another SETUP token, which leads to endxfer timeouts on all subsequent
>>> endpoints.
>>
>> Thanks for the captures. I think the problem here is because the dwc3
>> driver disables the control endpoint. It shouldn't do that.
>>
>> Can you try this:
>>
>> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
>> index ab725d2262d6..f0b9ea353620 100644
>> --- a/drivers/usb/dwc3/gadget.c
>> +++ b/drivers/usb/dwc3/gadget.c
>> @@ -1010,12 +1010,12 @@ static int __dwc3_gadget_ep_disable(struct
>> dwc3_ep *dep)
>> if (dep->flags & DWC3_EP_STALL)
>> __dwc3_gadget_ep_set_halt(dep, 0, false);
>>
>> - reg = dwc3_readl(dwc->regs, DWC3_DALEPENA);
>> - reg &= ~DWC3_DALEPENA_EP(dep->number);
>> - dwc3_writel(dwc->regs, DWC3_DALEPENA, reg);
>> -
>> - /* Clear out the ep descriptors for non-ep0 */
>> if (dep->number > 1) {
>> + reg = dwc3_readl(dwc->regs, DWC3_DALEPENA);
>> + reg &= ~DWC3_DALEPENA_EP(dep->number);
>> + dwc3_writel(dwc->regs, DWC3_DALEPENA, reg);
>> +
>> + /* Clear out the ep descriptors for non-ep0 */
>> dep->endpoint.comp_desc = NULL;
>> dep->endpoint.desc = NULL;
>> }
>>
> I was able to reproduce the endxfer timeout w/ the above change. I'm
> assuming you didn't want me to include any parts of my change while
> testing, right?
>

Right, please don't add additional code. I can't review knowing what
else was changed.

> Current sequence in dwc3_gadget_pullup(0) is that we should call
> dwc3_stop_active_transfers() before we call __dwc3_gadget_stop().
> (gadget stop will call the ep disable for EP[0] and EP[1]) This might
> be why the issue would still be occurring.
>
> The attached ftrace that captures a situation where a forced BUG will
> occur on the first instance of the timeout.
>
> [ 1573.687689437 0x724885c22] event (000020c0): ep0out: Transfer
> Not Ready [0] (Not Active) [Status Phase]
> [ 1573.687738707 0x724885fd3] dbg_send_ep_cmd: ep0out: cmd
> 'Start Transfer' [406] params 00000000 efffa000 00000000 --> status:
> Successful
> [ 1573.698040582 0x7248b6477] dbg_send_ep_cmd: ep1out: cmd 'End
> Transfer' [20c08] params 00000000 00000000 00000000 --> status: Timed Out
>
> We definitely started the STATUS phase, so host could have read it and
> sent the next SETUP packet while we were already in the
> dwc3_stop_active_transfers() loop.

Yeah, pullup() is another async call that can trigger the same problem.

[ 1573.687193134 0x7248836e8] dbg_send_ep_cmd: ep0out: cmd 'Start Transfer' [406] params 00000000 efffa000 00000000 --> status: Successful
[ 1573.687263291 0x724883c2b] event (0000c040): ep0out: Transfer Complete (sIL) [Setup Phase]
[ 1573.687287145 0x724883df6] dbg_trace_log_ctrl: Clear Interface Feature(Function Suspend)

Trace indicates that this is ClearFeature(Interface.FuncSuspend)

[ 1573.687372301 0x724884459] dbg_send_ep_cmd: ep0in: cmd 'Start Transfer' [406] params 00000000 efffa000 00000000 --> status: Successful
[ 1573.687400634 0x724884679] event (000010c2): ep0in: Transfer Not Ready [0] (Not Active) [Data Phase]
[ 1573.687471155 0x724884bc2] event (000090c2): ep0in: Transfer Not Ready [0] (Active) [Data Phase]
[ 1573.687495009 0x724884d8d] event (0000c042): ep0in: Transfer Complete (sIL) [Data Phase]
[ 1573.687544697 0x724885146] dbg_gadget_giveback: ep0out: req ffffff87a6768800 length 20/20 ZsI ==> 0

But there's data stage. Is this non-standard/vendor request?
We probably need to fix the tracepoint to properly print vendor
requests.

[ 1573.687593187 0x7248854e9] dbg_ep_queue: ep5in: req ffffff87a6769000 length 0/8 zsI ==> -115
[ 1573.687619645 0x7248856e6] dbg_prepare: ep5in: trb ffffffc05a97d1a0 (E27:D26) buf 00000000ee07f600 size 1x 8 ctrl 00000811 (Hlcs:sC:normal)
[ 1573.687660270 0x7248859f2] dbg_send_ep_cmd: ep5in: cmd 'Update Transfer' [b0007] params 00000000 00000000 00000000 --> status: Successful
[ 1573.687689437 0x724885c22] event (000020c0): ep0out: Transfer Not Ready [0] (Not Active) [Status Phase]
[ 1573.687738707 0x724885fd3] dbg_send_ep_cmd: ep0out: cmd 'Start Transfer' [406] params 00000000 efffa000 00000000 --> status: Successful

It's still in status stage, it never reached Setup phase.

[ 1573.698040582 0x7248b6477] dbg_send_ep_cmd: ep1out: cmd 'End Transfer' [20c08] params 00000000 00000000 00000000 --> status: Timed Out

That's why it's possible to time out here. The Setup Phase should
have been prepared before we can issue End Transfer.

I can't see where the pullup() begins as this log is missing register
read/write trace events. Looks like the wait_for_completion_timeout()
is insufficient. I assume it happens right after previous Setup
phase. There's no spin_lock, so the driver can proceed with the
new control request before it reaches dwc3_stop_active_transfers().

Can you try this. (yes, the code looks ugly right now, but it's just
to confirm my suspicion)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index ab725d2262d6..3b40411556ff 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -2506,6 +2506,8 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)

is_on = !!is_on;
dwc->softconnect = is_on;
+
+retry:
/*
* Per databook, when we want to stop the gadget, if a control transfer
* is still in process, complete it and get the core into setup phase.
@@ -2541,6 +2543,24 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
return 0;
}

+ if (!is_on) {
+ spin_lock_irqsave(&dwc->lock, flags);
+ if (dwc->ep0state != EP0_SETUP_PHASE) {
+ spin_unlock_irqrestore(&dwc->lock, flags);
+ goto retry;
+ }
+
+ /*
+ * In the Synopsis DesignWare Cores USB3 Databook Rev. 3.30a
+ * Section 4.1.8 Table 4-7, it states that for a device-initiated
+ * disconnect, the SW needs to ensure that it sends "a DEPENDXFER
+ * command for any active transfers" before clearing the RunStop
+ * bit.
+ */
+ dwc3_stop_active_transfers(dwc);
+ spin_unlock_irqrestore(&dwc->lock, flags);
+ }
+
/*
* Synchronize and disable any further event handling while controller
* is being enabled/disabled.
@@ -2553,14 +2573,6 @@ static int dwc3_gadget_pullup(struct usb_gadget *g, int is_on)
u32 count;

dwc->connected = false;
- /*
- * In the Synopsis DesignWare Cores USB3 Databook Rev. 3.30a
- * Section 4.1.8 Table 4-7, it states that for a device-initiated
- * disconnect, the SW needs to ensure that it sends "a DEPENDXFER
- * command for any active transfers" before clearing the RunStop
- * bit.
- */
- dwc3_stop_active_transfers(dwc);
__dwc3_gadget_stop(dwc);

/*

Thanks,
Thinh