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Thu, 30 Jul 2026 13:13:34 +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 OWQCO/5Na2qWVQAAD6G6ig (envelope-from ); Thu, 30 Jul 2026 13:13:34 +0000 Date: Thu, 30 Jul 2026 15:13:34 +0200 Message-ID: <877bmc39j5.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> 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-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)[-0.998]; 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)[suse.de:mid,imap1.dmz-prg2.suse.org:helo] X-Spam-Flag: NO X-Spam-Score: -3.30 X-Spam-Level: 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