ALSA: doc: usb-audio: Add doc for QUIRK_FLAG_IFB_SILENCE_ON_EMPTY

QUIRK_FLAG_IFB_SILENCE_ON_EMPTY was introduced into usb-audio before
without appropriate documentation, so add it.

Fixes: a23812004228 ("ALSA: usb-audio: add IFB_SILENCE_ON_EMPTY quirk for Behringer Flow 8")
Signed-off-by: Rong Zhang <i@rong.moe>
Link: https://patch.msgid.link/20260527-uac-quirk-get-cur-vol-v1-1-e9362b712e5e@rong.moe
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/Documentation/sound/alsa-configuration.rst b/Documentation/sound/alsa-configuration.rst
index f75f087639415dd171e18d06f2dc6db8def33aae..4b30cd63c5a5a200bcb21595577748222009ab0d 100644 (file)
--- a/Documentation/sound/alsa-configuration.rst
+++ b/Documentation/sound/alsa-configuration.rst
@@ -2383,6 +2383,12 @@ quirk_flags
           ``V(x) = k * x``; ``dB(x) = 20 * log10(x)``. Overrides bit 24
         * bit 28: ``mixer_capture_linear_vol``
           Similar to bit 27 but for capture streams. Overrides bit 25
+        * bit 29: ``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).
 
 This module supports multiple devices, autoprobe and hotplugging.