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Thu, 30 Jul 2026 16:03:49 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id tHl/NuV1a2pmfgAAD6G6ig (envelope-from ); Thu, 30 Jul 2026 16:03:49 +0000 Date: Thu, 30 Jul 2026 18:03:49 +0200 Message-ID: <87qzkk1n2y.wl-tiwai@suse.de> From: Takashi Iwai To: Mark Shi Cc: Takashi Iwai , Gordon Chen , linux-sound@vger.kernel.org, Jaroslav Kysela , linux-kernel@vger.kernel.org Subject: Re: [PATCH] ALSA: usb-audio: add IFB_SILENCE_ON_EMPTY quirk for Behringer Flow 8 In-Reply-To: References: <20260526072906.90106-1-chengordon326@gmail.com> <87bjbr6tth.wl-tiwai@suse.de> <875x1z6q0t.wl-tiwai@suse.de> <87a4r95007.wl-tiwai@suse.de> <877bmc39j5.wl-tiwai@suse.de> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Spam-Score: -3.30 X-Spam-Level: X-Spam-Flag: NO X-Spamd-Result: default: False [-3.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_ALL(0.00)[]; ARC_NA(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com,hotmail.com]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; FREEMAIL_TO(0.00)[hotmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FREEMAIL_CC(0.00)[suse.de,gmail.com,vger.kernel.org,perex.cz]; RCPT_COUNT_FIVE(0.00)[6]; FROM_HAS_DN(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:mid] On Thu, 30 Jul 2026 17:40:11 +0200, Mark Shi wrote: > > Hi Takashi, > > 在 2026/7/30 21:13, Takashi Iwai 写道: > > On Thu, 30 Jul 2026 14:33:44 +0200, > > Mark Shi wrote: > >> Hi Takashi, > >> > >>> On Wed, 29 Jul 2026 16:28:23 +0200, > >>> Mark Shi wrote: > >>>> Hi Takashi, > >>>> > >>>> On Tue, 28 Jul 2026 17:46:05 +0200, > >>>> Mark Shi wrote: > >>>> Hi Takashi, > >>>> 在 2026/7/28 23:02, Takashi Iwai 写道: > >>>> On Tue, 28 Jul 2026 16:27:35 +0200, > >>>> Mark Shi wrote: > >>>> Hi Gordon, > >>>> 在 2026/5/26 15:29, Gordon Chen > >>>> 写道: > >>>> The Behringer Flow 8 > >>>> (1397:050c) is an 8-channel USB mixer that > >>>> declares OUT EP 0x01 with implicit feedback from capture EP 0x81 via > >>>> its UAC2 endpoint companion descriptor. After 5-35 minutes of > >>>> continuous playback, the device occasionally returns a capture URB in > >>>> which every iso_frame_desc has a non-zero status (-EXDEV bursts, > >>>> visible as rate-limited "frame N active: -18" lines in dmesg from > >>>> pcm.c). > >>>> In that case > >>>> snd_usb_handle_sync_urb() at endpoint.c counts bytes==0 > >>>> and falls into the early "skip empty packets" return originally added > >>>> for M-Audio Fast Track Ultra. As a result the playback EP loses its > >>>> sole IFB-driven feeder and the OUT ring starves permanently: hw_ptr > >>>> stops advancing while substream state remains RUNNING. Only USB > >>>> re-enumeration recovers. > >>>> Three independent ftrace > >>>> captures (taken at the moment of stall via a > >>>> userspace watchdog) consistently show: > >>>> - 60-70 capture URB > >>>> completions in the 70ms window before the marker > >>>> - 0 retire_playback_urb / queue_pending_output_urbs / > >>>> snd_usb_endpoint_implicit_feedback_sink calls > >>>> - every usb_submit_urb in the window comes from > >>>> snd_complete_urb+0x64e (capture self-resubmit), none from the > >>>> queue_pending_output_urbs path > >>>> Add a new opt-in quirk > >>>> QUIRK_FLAG_IFB_SILENCE_ON_EMPTY: when set, the > >>>> early return is skipped and we fall through to enqueue a packet_info > >>>> whose packet_size[i] are all 0 (the existing loop already maps > >>>> status!=0 packets to size 0). prepare_outbound_urb then emits a > >>>> silence packet, the OUT ring keeps moving, and the device rides > >>>> through the glitch. > >>>> The default behaviour > >>>> (early return) is preserved for all existing > >>>> devices including M-Audio Fast Track Ultra. Only Flow 8 opts in here. > >>>> Cc: > >>>> stable@vger.kernel.org > >>>> Signed-off-by: Gordon Chen > >>>> > >>>> Device: Mechrevo WUJIE14Pro A-7BC4U > >>>> CPU: AMD Ryzen 7 7840HS (Codename "Phoenix") > >>>> Firmware Version: T140_PHX_V20 > >>>> Firmware Release Date: 2024.1.8 > >>>> Kernel version: 7.1.4 > >>>> In Linux kernel 7.1.4, I found > >>>> that my laptop couldn't wake up from S3 > >>>> suspend; I had to hold down the power button to force a shutdown and > >>>> then restart it. > >>>> Using `git bisect`, I discovered > >>>> that if I revert this patch, the > >>>> laptop resumes from S3 normally. > >>>> Do you have this USB-audio device > >>>> (Behringer Flow 8 with USB ID > >>>> 1397:050c)? The commit must be harmless unless you have this device. > >>>> That is, if you don't have this device, it's likely a false-positive > >>>> bisection result. > >>>> > >>>> thanks, > >>>> Takashi > >>>> I don't have that device, but I partially > >>>> reverted the code in that > >>>> section, and it went back to normal. > >>>> Hmm, that's odd. > >>>> Could you put a debug print what value does > >>>> ep->chip->quirk_flags > >>>> have on your device? > >>>> > >>>> thanks, > >>>> Takashi > >>>> I added `usb_audio_info`, compiled and booted, but `dmesg | > >>>> grep "quirk_flags" > >>>> ` returned no output. > >>> Then something wrong in your test :) > >>> > >>> Put another debug print at another place like the probe function, in > >>> order to verify whether the patched driver is really loaded, too. > >>> And, make sure that you're running the exactly patched kernel. > >>> > >>> > >>> Takashi > >> > >> I used the `printk` function to retrieve the `quirk_flags` for the > >> current function. Here is the output: > >> > >> ``` > >> > >> [   23.225719] snd-usb-audio: quirk_flags = 0x100800 > >> > > And what about ep->chip->quirk_flags at the place in question? Does > > it show the very same value? > > > > The value 0x100800 means that your device has the quirk bit 11 > > (QUIRK_TYPE_IFACE_DELAY) and bit 20 (QUIRK_TYPE_FORCE_IFACE_RESET), > > and they have nothing to do with the commit you're testing. > > > > > > thanks, > > Takashi > > I modified the output and added two log points for this purpose, and output: > > ``` > > [   23.355939] snd-usb-audio:snd_usb_endpoint_start() quirk_flags = 0x100800 > [   23.437401] snd-usb-audio:snd_usb_endpoint_start() quirk_flags = 0x100800 > [   67.813139] snd-usb-audio:snd_usb_endpoint_start() quirk_flags = 0x100800 > > ``` > > Regardless of whether I added a log point, > `snd_usb_endpoint_implicit_feedback_sink()` did not produce any > output. > > However, without the partial code rollback, during the 7.1.3–7.1.4 > period, I could only restore normal operation by disabling PCIe power > management using the "pcie_port_pm=off" kernel parameter (from > "amd_s2idle.py" script's report). > > Unfortunately for me, the platform returned to normal in version 7.1.5 > (even though I hadn't applied any patches) (T_T). This makes it > impossible for me to determine which side is at fault. Well, that must be a false-positive, as you couldn't get the debug print at the patch actually touching. Let us know if you can reproduce the issue reliably and it still points to this commit. thanks, Takashi