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for Behringer Flow 8 To: Takashi Iwai Cc: Gordon Chen , linux-sound@vger.kernel.org, Jaroslav Kysela , linux-kernel@vger.kernel.org References: <20260526072906.90106-1-chengordon326@gmail.com> <87bjbr6tth.wl-tiwai@suse.de> <875x1z6q0t.wl-tiwai@suse.de> <87a4r95007.wl-tiwai@suse.de> Content-Language: en-US From: Mark Shi In-Reply-To: <87a4r95007.wl-tiwai@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SE2P216CA0129.KORP216.PROD.OUTLOOK.COM (2603:1096:101:2c7::14) To OS3PR01MB8827.jpnprd01.prod.outlook.com (2603:1096:604:153::9) X-Microsoft-Original-Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: OS3PR01MB8827:EE_|OS3PR01MB8225:EE_ X-MS-Office365-Filtering-Correlation-Id: 859698a2-f730-4c60-7780-08deee36cdc8 X-Microsoft-Antispam: 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00000000-0000-0000-0000-000000000000 X-MS-Exchange-Transport-CrossTenantHeadersStamped: OS3PR01MB8225 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 ``` -- Best Regards, Mark Shi