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Tue, 28 Jul 2026 15:02:49 +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 kPwYG5nEaGolNwAAD6G6ig (envelope-from ); Tue, 28 Jul 2026 15:02:49 +0000 Date: Tue, 28 Jul 2026 17:02:34 +0200 Message-ID: <87bjbr6tth.wl-tiwai@suse.de> From: Takashi Iwai To: Mark Shi Cc: Gordon Chen , linux-sound@vger.kernel.org, Takashi Iwai , 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> 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=ISO-2022-JP X-Spamd-Result: default: False [-3.51 / 50.00]; BAYES_HAM(-3.00)[99.99%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-0.999]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_TO(0.00)[hotmail.com]; RCVD_VIA_SMTP_AUTH(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; TO_DN_SOME(0.00)[]; RCVD_TLS_ALL(0.00)[]; ARC_NA(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com,hotmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[gmail.com,vger.kernel.org,suse.de,perex.cz]; RCPT_COUNT_FIVE(0.00)[6]; FROM_EQ_ENVFROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:dkim,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_TRACE(0.00)[suse.de:+] X-Spam-Flag: NO X-Spam-Score: -3.51 X-Spam-Level: X-Rspamd-Queue-Id: 8D22E3E01 X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action 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