Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v10 0/6] Re-introduce TX FIFO resize for larger EP
 bursting
To:     Ferry Toth <fntoth@gmail.com>, Felipe Balbi <balbi@kernel.org>
Cc:     Wesley Cheng <wcheng@codeaurora.org>, gregkh@linuxfoundation.org,
        robh+dt@kernel.org, agross@kernel.org, bjorn.andersson@linaro.org,
        frowand.list@gmail.com, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, jackp@codeaurora.org,
        heikki.krogerus@linux.intel.com, andy.shevchenko@gmail.com,
        Ruslan Bilovol <ruslan.bilovol@gmail.com>
References: <1623923899-16759-1-git-send-email-wcheng@codeaurora.org>
 <ec8050c5-c013-4af6-b39e-69779c009a9c@codeaurora.org>
 <f5ed0ee7-e333-681f-0f1a-d0227562204b@gmail.com>
 <2e01c435-9ecc-4e3b-f55c-612a86667020@codeaurora.org>
 <2ae9fa6a-3bb1-3742-0dd3-59678bdd8643@gmail.com>
 <ebea75fe-5334-197b-f67a-cb6e1e30b39e@codeaurora.org>
 <bafa93bb-11e3-c8a5-e14a-b0a6d5695055@gmail.com> <87v951ldlt.fsf@kernel.org>
 <d9aef50c-4bd1-4957-13d8-0b6a14b9fcd0@gmail.com> <87pmv9l1dv.fsf@kernel.org>
 <9dc6cd83-17b9-7075-0934-6b9d41b6875d@gmail.com> <87a6mbudvc.fsf@kernel.org>
 <6e8bb4ad-fe68-ad36-7416-2b8e10b6ae96@gmail.com> <877dhev68a.fsf@kernel.org>
 <cca69e90-b0ef-00b8-75d3-3bf959a93b45@gmail.com> <874kchvcq0.fsf@kernel.org>
 <e59f1201-2aa2-9075-1f94-a6ae7a046dc1@gmail.com> <8735raj766.fsf@kernel.org>
 <b3417c2c-613b-8ef6-2e2d-6e2cf9a5d5fd@gmail.com>
 <b3e820f0-9c94-7cba-a248-3b2ec5378ab0@gmail.com>
 <d298df65-417b-f318-9374-b463a15d8308@ivitera.com>
 <a7d7f0dd-dfbb-5eef-d1da-8cbdab5fc4a7@gmail.com>
From:   Pavel Hofman <pavel.hofman@ivitera.com>
Message-ID: <c4e29ac0-1df1-3c64-1218-3687f07e7f77@ivitera.com>
Date:   Thu, 19 Aug 2021 23:04:50 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.2.1
MIME-Version: 1.0
In-Reply-To: <a7d7f0dd-dfbb-5eef-d1da-8cbdab5fc4a7@gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Precedence: bulk


Dne 19. 08. 21 v 22:10 Ferry Toth napsal(a):
> Hi
> 
> Op 19-08-2021 om 09:51 schreef Pavel Hofman:
>> Hi,
>>
>> Dne 18. 08. 21 v 21:07 Ferry Toth napsal(a):
>>> Hi,
>>>
>>> Op 18-08-2021 om 00:00 schreef Ferry Toth:
>>>> Hi,
>>>>
>>>> Op 16-08-2021 om 07:18 schreef Felipe Balbi:
>>>>> Hi,
>>>>>
>>>>> Ferry Toth <fntoth@gmail.com> writes:
>>>>>>> Ferry Toth <fntoth@gmail.com> writes:
>>>>>>>>>>> Ferry Toth <fntoth@gmail.com> writes:
>>>>>>>>>>>>>>>> Hardware name: Intel Corporation Merrifield/BODEGA BAY, 
>>>>>>>>>>>>>>>> BIOS 542
>>>>>>>>>>>>>>>> 2015.01.21:18.19.48
>>>>>>>>>>>>>>>> RIP: 0010:0x500000000
>>>>>>>>>>>>>>>> Code: Unable to access opcode bytes at RIP 0x4ffffffd6.
>>>>>>>>>>>>>>>> RSP: 0018:ffffa4d00045fc28 EFLAGS: 00010046
>>>>>>>>>>>>>>>> RAX: 0000000500000000 RBX: ffff8cd546aed200 RCX: 
>>>>>>>>>>>>>>>> 0000000000000000
>>>>>>>>>>>>>>>> RDX: 0000000000000000 RSI: ffff8cd547bfcae0 RDI: 
>>>>>>>>>>>>>>>> ffff8cd546aed200
>>>>>>>>>>>>>>>> RBP: ffff8cd547bfcae0 R08: 0000000000000000 R09: 
>>>>>>>>>>>>>>>> 0000000000000001
>>>>>>>>>>>>>>>> R10: ffff8cd541fd28c0 R11: 0000000000000000 R12: 
>>>>>>>>>>>>>>>> ffff8cd547342828
>>>>>>>>>>>>>>>> R13: ffff8cd546aed248 R14: 0000000000000000 R15: 
>>>>>>>>>>>>>>>> ffff8cd548b1d000
>>>>>>>>>>>>>>>> FS:  0000000000000000(0000) GS:ffff8cd57e200000(0000) 
>>>>>>>>>>>>>>>> knlGS:0000000000000000
>>>>>>>>>>>>>>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>>>>>>>>>>>>> CR2: 0000000500000000 CR3: 000000000311e000 CR4: 
>>>>>>>>>>>>>>>> 00000000001006f0
>>>>>>>>>>>>>>>> Call Trace:
>>>>>>>>>>>>>>>>         ? dwc3_remove_requests.constprop.0+0x14d/0x170
>>>>>>>>>>>>>>>>         ? __dwc3_gadget_ep_disable+0x7a/0x160
>>>>>>>>>>>>>>>>         ? dwc3_gadget_ep_disable+0x3d/0xd0
>>>>>>>>>>>>>>>>         ? usb_ep_disable+0x1c/0x
>>>>>>>>>>>>>>>>         ? u_audio_stop_capture+0x79/0x120 [u_audio]
>>>>>>>>>>>>>>>>         ? afunc_set_alt+0x73/0x80 [usb_f_uac2]
>>>>>>>>> So this is triggered by a SetInterface request...
>>>>>>>>>
>>>>>>>>>>>>>>>>         ? composite_setup+0x224/0x1b90 [libcomposite]
>>>>>>>>>>>>>>>>         ? __dwc3_gadget_kick_transfer+0x160/0x400
>>>>>>>>>>>>>>>>         ? dwc3_gadget_ep_queue+0xf3/0x1a0
>>>>>>>>>>>>>>>>         ? configfs_composite_setup+0x6b/0x90 [libcomposite]
>>>>>>>>>>>>>>>>         ? configfs_composite_setup+0x6b/0x90 [libcomposite]
>>>>>>>>>>>>>>>>         ? dwc3_ep0_interrupt+0x459/0xa40
>>>>>>>>>>>>>>>>         ? dwc3_thread_interrupt+0x8ee/0xf40
>>>>>>>>>>>>>>>>         ? __schedule+0x235/0x6c0
>>>>>>>>>>>>>>>>         ? disable_irq_nosync+0x10/0x10
>>>>>>>>>>>>>>>>         ? irq_thread_fn+0x1b/0x60
>>>>>>>>>>>>>>>>         ? irq_thread+0xc0/0x160
>>>>>>>>>>>>>>>>         ? irq_thread_check_affinity+0x70/0x70
>>>>>>>>>>>>>>>>         ? irq_forced_thread_fn+0x70/0x70
>>>>>>>>>>>>>>>>         ? kthread+0x122/0x140
>>>>>>>>>>>>>>>>         ? set_kthread_struct+0x40/0x40
>>>>>>>>>>>>>>>>         ? ret_from_fork+0x22/0x30
>>>>>>>>>>>>>>> Do you mind enabling dwc3 traces and collecting them? 
>>>>>>>>>>>>>>> Trying to figure
>>>>>>>>>>>>>>> out how we got here.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I'll try if I can get the same error by booting with USB 
>>>>>>>>>>>>>> in host mode
>>>>>>>>>>>>>> and then switch to device mode. If so I can enable traces 
>>>>>>>>>>>>>> and collect as
>>>>>>>>>>>>>> you explained me before.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I'll try before monday, as then I fly for a holiday and 
>>>>>>>>>>>>>> will not be
>>>>>>>>>>>>>> available before rc5.
>>>>>>>>>>>>> you can enable all of those with kernel cmdline :-)
>>>>>>>>>>>>>
>>>>>>>>>>>>> https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html 
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> you need ftrace_dump_on_oops=1 and also need the correct 
>>>>>>>>>>>>> options on
>>>>>>>>>>>>> trace_buf_size and trace_event.
>>>>>>>>>>>>>
>>>>>>>>>>>> On Edison-Arduino I have a switch to go to device mode, 
>>>>>>>>>>>> after which
>>>>>>>>>>>> udev triggers a script configure gadgets through configfs.
>>>>>>>>>>>>
>>>>>>>>>>>> I tried to log following these instructions:
>>>>>>>>>>>>
>>>>>>>>>>>> https://www.kernel.org/doc/html/latest/driver-api/usb/dwc3.html#reporting-bugs 
>>>>>>>>>>>> <https://www.kernel.org/doc/html/latest/driver-api/usb/dwc3.html#reporting-bugs> 
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> Unfortunately the kernel crashes so badly I can not get to 
>>>>>>>>>>>> the ` cp
>>>>>>>>>>>> /t/trace /root/trace.txt` line (after a while the watchdog 
>>>>>>>>>>>> kicks).
>>>>>>>>>>>>
>>>>>>>>>>>> What to do next?
>>>>>>>>>>> Pass ftrace_dump_on_oops to kernel cmdline.
>>>>>>>>>>>
>>>>>>>>>> No sure if I did this right, on oops everything is pushed to 
>>>>>>>>>> console
>>>>>>>>>> (115k2 serial), I hope nothing essential is lost.
>>>>>>>>>>
>>>>>>>>>> I copied the screen buffer to file see attached.
>>>>>>>>> Thank you, I bet it took quite a some time :-) Anyway, looking at
>>>>>>>>> the logs around Set Interface requests, we can track every 
>>>>>>>>> endpoint
>>>>>>>>> that's disabled. I'll take a guess and assume we're failing at 
>>>>>>>>> the last
>>>>>>>>> Set Interface, that means we should have something odd with 
>>>>>>>>> ep6in, but
>>>>>>>>> everything looks fine in the trace output:
>>>>>>>>>
>>>>>>>>> [   75.823107] irq/14-d-596       0d... 42789194us : 
>>>>>>>>> dwc3_gadget_ep_enable: ep6in: mps 192/346 streams 16 burst 0 
>>>>>>>>> ring 0/0 flags E:swbp:<
>>>>>>>>> [   75.835472] irq/14-d-596       0d... 42789198us : 
>>>>>>>>> dwc3_alloc_request: ep6in: req 0000000002c71409 length 0/0 zsI 
>>>>>>>>> ==> 0
>>>>>>>>> [   75.846416] irq/14-d-596       0d... 42789202us : 
>>>>>>>>> dwc3_ep_queue: ep6in: req 0000000002c71409 length 0/192 zsI ==> 
>>>>>>>>> -115
>>>>>>>>> [   75.857360] irq/14-d-596       0d... 42789204us : 
>>>>>>>>> dwc3_alloc_request: ep6in: req 00000000a324f5d0 length 0/0 zsI 
>>>>>>>>> ==> 0
>>>>>>>>> [   75.868301] irq/14-d-596       0d... 42789206us : 
>>>>>>>>> dwc3_ep_queue: ep6in: req 00000000a324f5d0 length 0/192 zsI ==> 
>>>>>>>>> -115
>>>>>>>>> [   75.879244] irq/14-d-596       0d... 42789209us : 
>>>>>>>>> dwc3_event: event (000020c2): ep0in: Transfer Not Ready [0] 
>>>>>>>>> (Not Active) [Status Phase]
>>>>>>>>> [   75.891880] irq/14-d-596       0d... 42789211us : 
>>>>>>>>> dwc3_prepare_trb: ep0in: trb 000000004c0ae319 (E0:D0) buf 
>>>>>>>>> 000000001bded000 size 0 ctrl 00000c33 (HLcs:SC:status2)
>>>>>>>>> [   75.989131] irq/14-d-596       0d... 42789224us : 
>>>>>>>>> dwc3_gadget_ep_cmd: ep0in: cmd 'Start Transfer' [406] params 
>>>>>>>>> 00000000 1bded000 00000000 --> status: Successful
>>>>>>>>> [   76.096261] irq/14-d-596       0d... 42789272us : 
>>>>>>>>> dwc3_event: event (0000c042): ep0in: Transfer Complete (sIL) 
>>>>>>>>> [Status Phase]
>>>>>>>>> [   76.107834] irq/14-d-596       0d... 42789275us : 
>>>>>>>>> dwc3_complete_trb: ep0out: trb 000000004c0ae319 (E0:D0) buf 
>>>>>>>>> 000000001bded000 size 0 ctrl 00000c32 (hLcs:SC:status2)
>>>>>>>>> [   76.122944] irq/14-d-596       0d... 42789277us : 
>>>>>>>>> dwc3_gadget_giveback: ep0out: req 00000000cb1bd3cd length 0/0 
>>>>>>>>> zsI ==> 0
>>>>>>>>> [   76.134160] irq/14-d-596       0d... 42789280us : 
>>>>>>>>> dwc3_prepare_trb: ep0out: trb 000000004c0ae319 (E0:D0) buf 
>>>>>>>>> 000000001bded000 size 8 ctrl 00000c23 (HLcs:SC:setup)
>>>>>>>>> [   76.231322] irq/14-d-596       0d... 42789292us : 
>>>>>>>>> dwc3_gadget_ep_cmd: ep0out: cmd 'Start Transfer' [406] params 
>>>>>>>>> 00000000 1bded000 00000000 --> status: Successful
>>>>>>>>> [   76.297418] kworker/-23        0d... 42789670us : 
>>>>>>>>> dwc3_ep_queue: ep3in: req 0000000029586135 length 0/96 ZsI ==> 
>>>>>>>>> -115
>>>>>>>>> [   76.308278] kworker/-23        0d... 42789695us : 
>>>>>>>>> dwc3_prepare_trb: ep3in: trb 00000000b81213d6 (E1:D0) buf 
>>>>>>>>> 0000000003b7a800 size 96 ctrl 00000811 (Hlcs:sC:normal)
>>>>>>>>> [   76.395294] kworker/-23        0d... 42789707us : 
>>>>>>>>> dwc3_gadget_ep_cmd: ep3in: cmd 'Update Transfer' [60007] params 
>>>>>>>>> 00000000 00000000 00000000 --> status: Successful
>>>>>>>>> [   76.471900] irq/14-d-596       0d... 42789842us : 
>>>>>>>>> dwc3_event: event (0000c040): ep0out: Transfer Complete (sIL) 
>>>>>>>>> [Setup Phase]
>>>>>>>>> [   76.489308] irq/14-d-596       0d... 42789845us : 
>>>>>>>>> dwc3_ctrl_req: Set Interface(Intf = 5, Alt.Setting = 0)
>>>>>>>>> [   76.505650] irq/14-d-596       0d... 42789851us : 
>>>>>>>>> dwc3_ep_dequeue: ep6in: req 0000000002c71409 length 0/192 zsI 
>>>>>>>>> ==> -115
>>>>>>>>> [   76.523315] irq/14-d-596       0d... 42789854us : 
>>>>>>>>> dwc3_gadget_giveback: ep6in: req 0000000002c71409 length 0/192 
>>>>>>>>> zsI ==> -104
>>>>>>>>> [   76.541427] irq/14-d-596       0d... 42789857us : 
>>>>>>>>> dwc3_free_request: ep6in: req 0000000002c71409 length 0/192 zsI 
>>>>>>>>> ==> -104
>>>>>>>>> [   76.559267] irq/14-d-596       0d... 42789859us : 
>>>>>>>>> dwc3_ep_dequeue: ep6in: req 00000000a324f5d0 length 0/192 zsI 
>>>>>>>>> ==> -115
>>>>>>>>> [   76.576937] irq/14-d-596       0d... 42789861us : 
>>>>>>>>> dwc3_gadget_giveback: ep6in: req 00000000a324f5d0 length 0/192 
>>>>>>>>> zsI ==> -104
>>>>>>>>> [   76.595046] irq/14-d-596       0d... 42789862us : 
>>>>>>>>> dwc3_free_request: ep6in: req 00000000a324f5d0 length 0/192 zsI 
>>>>>>>>> ==> -104
>>>>>>>>> [   76.612892] irq/14-d-596       0d... 42789865us : 
>>>>>>>>> dwc3_gadget_ep_disable: ep6in: mps 192/346 streams 16 burst 0 
>>>>>>>>> ring 0/0 flags E:swbp:<
>>>>>>>>> [   76.665535] irq/14-d-596       0d... 42789873us : 
>>>>>>>>> dwc3_event: event (000020c2): ep0in: Transfer Not Ready [0] 
>>>>>>>>> (Not Active) [Status Phase]
>>>>>>>>> [   76.684716] irq/14-d-596       0d... 42789875us : 
>>>>>>>>> dwc3_prepare_trb: ep0in: trb 000000004c0ae319 (E0:D0) buf 
>>>>>>>>> 000000001bded000 size 0 ctrl 00000c33 (HLcs:SC:status2)
>>>>>>>>> [   76.819195] irq/14-d-596       0d... 42789886us : 
>>>>>>>>> dwc3_gadget_ep_cmd: ep0in: cmd 'Start Transfer' [406] params 
>>>>>>>>> 00000000 1bded000 00000000 --> status: Successful
>>>>>>>>> [   76.926324] irq/14-d-596       0d... 42789930us : 
>>>>>>>>> dwc3_event: event (0000c042): ep0in: Transfer Complete (sIL) 
>>>>>>>>> [Status Phase]
>>>>>>>>> [   76.937892] irq/14-d-596       0d... 42789933us : 
>>>>>>>>> dwc3_complete_trb: ep0out: trb 000000004c0ae319 (E0:D0) buf 
>>>>>>>>> 000000001bded000 size 0 ctrl 00000c32 (hLcs:SC:status2)
>>>>>>>>> [   76.953003] irq/14-d-596       0d... 42789935us : 
>>>>>>>>> dwc3_gadget_giveback: ep0out: req 00000000cb1bd3cd length 0/0 
>>>>>>>>> zsI ==> 0
>>>>>>>>> [   76.964217] irq/14-d-596       0d... 42789938us : 
>>>>>>>>> dwc3_prepare_trb: ep0out: trb 000000004c0ae319 (E0:D0) buf 
>>>>>>>>> 000000001bded000 size 8 ctrl 00000c23 (HLcs:SC:setup)
>>>>>>>>> [   77.061379] irq/14-d-596       0d... 42789950us : 
>>>>>>>>> dwc3_gadget_ep_cmd: ep0out: cmd 'Start Transfer' [406] params 
>>>>>>>>> 00000000 1bded000 00000000 --> status: Successful
>>>>>>>>> [   77.168595] irq/14-d-596       0d... 42790509us : 
>>>>>>>>> dwc3_event: event (0000c040): ep0out: Transfer Complete (sIL) 
>>>>>>>>> [Setup Phase]
>>>>>>>>> [   77.180159] irq/14-d-596       0d... 42790512us : 
>>>>>>>>> dwc3_ctrl_req: Get String Descriptor(Index = 18, Length = 255)
>>>>>>>>> [   77.190578] irq/14-d-596       0d... 42790537us : 
>>>>>>>>> dwc3_prepare_trb: ep0in: trb 000000004c0ae319 (E0:D0) buf 
>>>>>>>>> 0000000003b68000 size 36 ctrl 00000c53 (HLcs:SC:data)
>>>>>>>>> [   77.287648] irq/14-d-596       0d... 42790550us : 
>>>>>>>>> dwc3_gadget_ep_cmd: ep0in: cmd 'Start Transfer' [406] params 
>>>>>>>>> 00000000 1bded000 00000000 --> status: Successful
>>>>>>>>> [   77.333107] irq/14-d-596       0d... 42790557us : 
>>>>>>>>> dwc3_event: event (000010c2): ep0in: Transfer Not Ready [0] 
>>>>>>>>> (Not Active) [Data Phase]
>>>>>>>>> [   77.407223] irq/14-d-596       0d... 42790575us : 
>>>>>>>>> dwc3_event: event (000090c2): ep0in: Transfer Not Ready [0] 
>>>>>>>>> (Active) [Data Phase]
>>>>>>>>> [   77.480985] irq/14-d-596       0d... 42790588us : 
>>>>>>>>> dwc3_event: event (0000c042): ep0in: Transfer Complete (sIL) 
>>>>>>>>> [Data Phase]
>>>>>>>>> [   77.492376] irq/14-d-596       0d... 42790590us : 
>>>>>>>>> dwc3_complete_trb: ep0out: trb 000000004c0ae319 (E0:D0) buf 
>>>>>>>>> 0000000003b68000 size 0 ctrl 00000c52 (hLcs:SC:data)
>>>>>>>>> [   77.507221] irq/14-d-596       0d... 42790595us : 
>>>>>>>>> dwc3_gadget_giveback: ep0out: req 00000000cb1bd3cd length 36/36 
>>>>>>>>> ZsI ==> 0
>>>>>>>>> [   77.518609] irq/14-d-596       0d... 42790597us : 
>>>>>>>>> dwc3_event: event (000020c0): ep0out: Transfer Not Ready [0] 
>>>>>>>>> (Not Active) [Status Phase]
>>>>>>>>> [   77.531332] irq/14-d-596       0d... 42790598us : 
>>>>>>>>> dwc3_prepare_trb: ep0out: trb 000000004c0ae319 (E0:D0) buf 
>>>>>>>>> 000000001bded000 size 0 ctrl 00000c43 (HLcs:SC:status3)
>>>>>>>>> [   77.628669] irq/14-d-596       0d... 42790609us : 
>>>>>>>>> dwc3_gadget_ep_cmd: ep0out: cmd 'Start Transfer' [406] params 
>>>>>>>>> 00000000 1bded000 00000000 --> status: Successful
>>>>>>>>>
>>>>>>>>> Do you mind adding a few prints in dwc3_remove_requests to tell 
>>>>>>>>> us which
>>>>>>>>> endpoint is being processed? Then we'll know for sure which one 
>>>>>>>>> caused
>>>>>>>>> the crash.
>>>>>>>>>
>>>>>>>> I wouldn't mind but am leaving on a holiday, won't have time 
>>>>>>>> until 6 aug.
>>>>>>> not a problem, we'll still be here when you're back :-)
>>>>>> Well, let's go then :-)
>>>>>>
>>>>>> To get back in the mood I have retested 5.13.0, 5.14.0-rc1, 
>>>>>> 5.14.0-rc2
>>>>>> and 5.14.0-rc5.
>>>>>>
>>>>>> I find that 5.13.0 works fine, and the issue starts from 5.14.0-rc1.
>>>>> That's great finding. We have a bisection point. There are a total of
>>>>> 13764 commits between v5.13 and v5.14-rc1
>>>>>
>>>>>     $ git rev-list  --count v5.13..v5.14-rc1
>>>>>     13764
>>>>>
>>>>> git bisect should find the offending commit in at most 14 tries. 
>>>>> That's
>>>>> not too bad.
>>>> I correctly guesstimated that the problem got introduced by the usb 
>>>> merge 79160a60
>>>>
>>>> "Merge tag 'usb-5.14-rc1' of 
>>>> git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb"
>>>>
>>>> 116 commits(7 bisects).
>>>>
>>>> 24f779dac8f3efb9629adc0e486914d93dc45517 is the first bad commit
>>>>
>>>> "usb: gadget: f_uac2/u_audio: add feedback endpoint support"
>>>>
>>>> Ruslan's 3 patches are related to each other so I reverted all three 
>>>> 24f779da...e89bb428 and applied the reverts to rc1.
>>>>
>>>> I can confirm this indeed resolves the problem in rc1.
>>>>
>>>> Is late now, tomorrow evening I will apply the reverts to rc6.
>>>
>>> With these reverts rc6 works fine as well.
>>>
>>> So, where do we go from here?
>>>
>>
>> I know the patches have been tested on dwc2 (by me and others).  I do 
>> not know if Ruslan or Jerome tested them on dwc3 but probably not. 
>> Ruslan has talked about RPi (my case too) and BeagleboneBlack, both 
>> with dwc2. Perhaps the dwc2 behaves a bit differently than dwc3?
>>
>> The patches add a new EP-IN for async feedback. I am sorry I have not 
>> followed your long thread (it started as unrelated to uac). Does the 
>> problem appear with f_uac1 or f_uac2? Please how have you reached the 
>> above problem?
> 
> I'm sorry too. I first believed the issue was related to the patch 
> mentioned in the subject line.
> 
> The problem appaers with f_uac2. I bost Edison_Arduino board in host 
> mode (there is a switch allowing to select host/device mode). When 
> flipping the switch to device mode udev run a script:
> But as I am using configfs (excerpt follows) and just disabling the last 
> 2 line resolves the issue, I'm guessing uac2 is the issue. Or exceeding 
> the available resources.
> 
> # Create directory structure
> mkdir "${GADGET_BASE_DIR}"
> cd "${GADGET_BASE_DIR}"
> mkdir -p configs/c.1/strings/0x409
> mkdir -p strings/0x409
> 
> # Serial device
> mkdir functions/gser.usb0
> ln -s functions/gser.usb0 configs/c.1/
> ###
> 
> # Ethernet device
> mkdir functions/eem.usb0
> echo "${DEV_ETH_ADDR}" > functions/eem.usb0/dev_addr
> echo "${HOST_ETH_ADDR}" > functions/eem.usb0/host_addr
> ln -s functions/eem.usb0 configs/c.1/
> 
> # Mass Storage device
> mkdir functions/mass_storage.usb0
> echo 1 > functions/mass_storage.usb0/stall
> echo 0 > functions/mass_storage.usb0/lun.0/cdrom
> echo 0 > functions/mass_storage.usb0/lun.0/ro
> echo 0 > functions/mass_storage.usb0/lun.0/nofua
> echo "${USBDISK}" > functions/mass_storage.usb0/lun.0/file
> ln -s functions/mass_storage.usb0 configs/c.1/
> 
> # UAC2 device
> mkdir functions/uac2.usb0
> ln -s functions/uac2.usb0 configs/c.1
> ....
> 

As you say, could perhaps the reason be that the extra EP-IN added in 
those patches (previously 1, now 2 with the default config you use) 
exceeds your EP-IN max count or available fifos somehow?  You have a 
number of functions initialized. If you change the load order of the 
functions, do you get the error later with a different function? Just 
guessing...

You should be able to switch the default async EP-OUT (which configures 
the new feedback EP-IN ) to adaptive EP-OUT (which requires no feedback 
EP) with c_sync=8 parameter of f_uac2.

https://elixir.bootlin.com/linux/v5.14-rc6/source/drivers/usb/gadget/function/f_uac2.c#L47

https://elixir.bootlin.com/linux/v5.14-rc6/source/drivers/usb/gadget/function/f_uac2.c#L830

https://elixir.bootlin.com/linux/v5.14-rc6/source/include/uapi/linux/usb/ch9.h#L453

Does that fix the problem?

Thanks,

Pavel.