diff options
| author | Gordon Chen <chengordon326@gmail.com> | 2026-05-26 15:29:06 +0800 |
|---|---|---|
| committer | Takashi Iwai <tiwai@suse.de> | 2026-05-26 16:28:05 +0200 |
| commit | a23812004228d4b041a858b927db787a7ff80f50 (patch) | |
| tree | e30090b1244597e984358d1b97f0fdc66a88ef41 | |
| parent | dd1bfaf9413e9c8a0fcfb45dcb735c6768a45251 (diff) | |
| download | linux-next-history-a23812004228.tar.gz | |
ALSA: usb-audio: add IFB_SILENCE_ON_EMPTY quirk for Behringer Flow 8
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 <chengordon326@gmail.com>
Link: https://patch.msgid.link/20260526072906.90106-1-chengordon326@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
| -rw-r--r-- | sound/usb/endpoint.c | 10 | ||||
| -rw-r--r-- | sound/usb/quirks.c | 3 | ||||
| -rw-r--r-- | sound/usb/usbaudio.h | 8 |
3 files changed, 20 insertions, 1 deletions
diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c index 6fbcb117555c6..24cd7692bd01c 100644 --- a/sound/usb/endpoint.c +++ b/sound/usb/endpoint.c @@ -1780,8 +1780,16 @@ static void snd_usb_handle_sync_urb(struct snd_usb_endpoint *ep, /* * skip empty packets. At least M-Audio's Fast Track Ultra stops * streaming once it received a 0-byte OUT URB + * + * However, on devices where bytes==0 means every sync-source + * packet errored (e.g. Behringer Flow 8 returning -EXDEV bursts + * for entire capture URBs), an unconditional return starves the + * IFB-fed OUT ring permanently. Such devices set + * QUIRK_FLAG_IFB_SILENCE_ON_EMPTY to fall through and enqueue a + * packet_info with size 0 packets, so playback emits silence + * and the OUT ring keeps moving. */ - if (bytes == 0) + if (bytes == 0 && !(ep->chip->quirk_flags & QUIRK_FLAG_IFB_SILENCE_ON_EMPTY)) return; spin_lock_irqsave(&ep->lock, flags); diff --git a/sound/usb/quirks.c b/sound/usb/quirks.c index 31cbe383ae658..e2c95be38aca4 100644 --- a/sound/usb/quirks.c +++ b/sound/usb/quirks.c @@ -2365,6 +2365,8 @@ static const struct usb_audio_quirk_flags_table quirk_flags_table[] = { QUIRK_FLAG_PLAYBACK_FIRST | QUIRK_FLAG_GENERIC_IMPLICIT_FB), DEVICE_FLG(0x1397, 0x0509, /* Behringer UMC404HD */ QUIRK_FLAG_PLAYBACK_FIRST | QUIRK_FLAG_GENERIC_IMPLICIT_FB), + DEVICE_FLG(0x1397, 0x050c, /* Behringer Flow 8 */ + QUIRK_FLAG_IFB_SILENCE_ON_EMPTY), DEVICE_FLG(0x13e5, 0x0001, /* Serato Phono */ QUIRK_FLAG_IGNORE_CTL_ERROR), DEVICE_FLG(0x152a, 0x880a, /* NeuralDSP Quad Cortex */ @@ -2602,6 +2604,7 @@ static const char *const snd_usb_audio_quirk_flag_names[] = { QUIRK_STRING_ENTRY(SKIP_IFACE_SETUP), QUIRK_STRING_ENTRY(MIXER_PLAYBACK_LINEAR_VOL), QUIRK_STRING_ENTRY(MIXER_CAPTURE_LINEAR_VOL), + QUIRK_STRING_ENTRY(IFB_SILENCE_ON_EMPTY), NULL }; diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h index 58fd07f8c3c97..9afcad8f143a0 100644 --- a/sound/usb/usbaudio.h +++ b/sound/usb/usbaudio.h @@ -236,6 +236,12 @@ extern bool snd_usb_skip_validation; * QUIRK_FLAG_MIXER_CAPTURE_LINEAR_VOL * Similar to QUIRK_FLAG_MIXER_PLAYBACK_LINEAR_VOL, but for capture streams. * Overrides QUIRK_FLAG_MIXER_CAPTURE_MIN_MUTE + * QUIRK_FLAG_IFB_SILENCE_ON_EMPTY + * In implicit feedback mode, when an entire capture URB returns with + * all iso_frame_desc[i].status != 0 (bytes==0), do not silently return + * from snd_usb_handle_sync_urb. Instead fall through and enqueue a + * packet_info containing only size-0 packets, so the OUT ring keeps + * moving (emits silence). Needed by Behringer Flow 8 (1397:050c). */ enum { @@ -268,6 +274,7 @@ enum { QUIRK_TYPE_SKIP_IFACE_SETUP = 26, QUIRK_TYPE_MIXER_PLAYBACK_LINEAR_VOL = 27, QUIRK_TYPE_MIXER_CAPTURE_LINEAR_VOL = 28, + QUIRK_TYPE_IFB_SILENCE_ON_EMPTY = 29, /* Please also edit snd_usb_audio_quirk_flag_names */ }; @@ -302,5 +309,6 @@ enum { #define QUIRK_FLAG_SKIP_IFACE_SETUP QUIRK_FLAG(SKIP_IFACE_SETUP) #define QUIRK_FLAG_MIXER_PLAYBACK_LINEAR_VOL QUIRK_FLAG(MIXER_PLAYBACK_LINEAR_VOL) #define QUIRK_FLAG_MIXER_CAPTURE_LINEAR_VOL QUIRK_FLAG(MIXER_CAPTURE_LINEAR_VOL) +#define QUIRK_FLAG_IFB_SILENCE_ON_EMPTY QUIRK_FLAG(IFB_SILENCE_ON_EMPTY) #endif /* __USBAUDIO_H */ |