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Tue, 28 Jul 2026 14:27:42 +0000 Received: from OS3PR01MB8827.jpnprd01.prod.outlook.com ([fe80::4bc9:630:cec7:d11f]) by OS3PR01MB8827.jpnprd01.prod.outlook.com ([fe80::4bc9:630:cec7:d11f%6]) with mapi id 15.21.0270.009; Tue, 28 Jul 2026 14:27:42 +0000 Message-ID: Date: Tue, 28 Jul 2026 22:27:35 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] ALSA: usb-audio: add IFB_SILENCE_ON_EMPTY quirk for Behringer Flow 8 To: Gordon Chen , linux-sound@vger.kernel.org Cc: Takashi Iwai , Jaroslav Kysela , linux-kernel@vger.kernel.org References: <20260526072906.90106-1-chengordon326@gmail.com> Content-Language: en-US From: Mark Shi In-Reply-To: <20260526072906.90106-1-chengordon326@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SI2P153CA0033.APCP153.PROD.OUTLOOK.COM (2603:1096:4:190::21) To OS3PR01MB8827.jpnprd01.prod.outlook.com (2603:1096:604:153::9) X-Microsoft-Original-Message-ID: <3d2721f9-9904-42c1-8095-21457a8c7b5f@hotmail.com> 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_|TY7PR01MB14890:EE_ X-MS-Office365-Filtering-Correlation-Id: e245f8b8-8867-46f6-a128-08deecb4615d X-Microsoft-Antispam: BCL:0;ARA:14566002|15080799012|24021099003|5072599009|25010399006|41001999006|23021999003|6090799003|37011999003|8022599003|19110799012|8060799015|440099028|3412199025|3071699003; 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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. Best Regards, Mark Shi