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Tue, 07 Jul 2026 11:32:08 -0700 (PDT) From: Agustin Luzardo To: perex@perex.cz, tiwai@suse.com Cc: linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, Agustin Luzardo Subject: [PATCH] ALSA: usb-audio: Do not drop per-channel feature controls marked get_cur_broken Date: Tue, 7 Jul 2026 15:31:33 -0300 Message-ID: <20260707183133.8113-1-agustinluzardo09@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260705184227.113588-1-agustinluzardo09@gmail.com> References: <20260705184227.113588-1-agustinluzardo09@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When a per-channel Feature Unit control (e.g. a stereo PCM Playback Volume control) hits the sticky-mixer check during get_min_max_with_quirks(), and the device carries QUIRK_FLAG_MIXER_GET_CUR_BROKEN, the sticky check marks the control as cval->get_cur_broken and returns -ENXIO instead of disabling it outright. However, __build_feature_ctl() does not know about this and treats any negative return other than -EAGAIN as fatal, discarding the kcontrol entirely: if ((ret < 0 && ret != -EAGAIN) || cval->max <= cval->min) { ... snd_ctl_free_one(kctl); return; } For a stereo device where only some channels trip the sticky check, this silently drops the per-channel (stereo) control while the master-only control (built separately, without going through the same channel-specific GET_CUR negotiation) survives. The result is that the user is left with a single mono/master volume control instead of the independent per-channel controls the device actually supports, with no visible error (usb_audio_dbg is typically compiled out). This was observed on a Weltrend Semiconductor 040b:0897 device (sold as the Redragon H510-PRO Wireless headset), which reports a genuine stereo Feature Unit (bNrChannels = 2, bmaControls with Volume set for both channels) but ends up exposing only a single-channel "PCM Playback Volume" control once QUIRK_FLAG_MIXER_GET_CUR_BROKEN is applied for that device. Skip the discard when the control was already marked get_cur_broken, as long as a sane range was otherwise established. Signed-off-by: Agustin Luzardo --- sound/usb/mixer.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c index 0000000..0000000 100644 --- a/sound/usb/mixer.c +++ b/sound/usb/mixer.c @@ -1970,8 +1970,10 @@ static void __build_feature_ctl(struct usb_mixer_interface *mixer, /* get min/max values */ ret = get_min_max_with_quirks(cval, 0, kctl); - /* skip a bogus volume range */ - if ((ret < 0 && ret != -EAGAIN) || cval->max <= cval->min) { + /* skip a bogus volume range, unless the sticky check already + * marked this control as usable via the driver's cached value + * (QUIRK_FLAG_MIXER_GET_CUR_BROKEN) */ + if ((ret < 0 && ret != -EAGAIN && !cval->get_cur_broken) || + cval->max <= cval->min) { usb_audio_dbg(mixer->chip, "[%d] FU [%s] skipped due to invalid volume\n", cval->head.id, kctl->id.name); -- 2.46.1