[PATCH 3/9] ALSA: usb-audio: Improve volume range checks

Rong Zhang
2026-03-01T21:37:57Z

Currently the volume range check is only meant to discover quirky
microphone on webcam devices and facing these issues:

- The check is only meaningful for dB volume, but it doesn't check if
the TLV callback is the corresponding one
- A common quirky pattern "val = 0/100/1" doesn't trigger any warning
- Some modern devices trigger the check, but they are legit
- The warning message doesn't apply to some quirky messages with linear
volume
- The term "range" in the warning message is confusing. At readers'
first glance it should be (max - min), but it turns out to be
((max - min) / res)

Solve these issues by improving the checking logic to:

- Ignore mixers with non-dB TLV
- Warn on unlikely small volume ranges (max - min < 256)
- Add some heuristics to determine if the volume range is unlikely big
- Rephrase the warning message to mention linear volume
- Rephrase the warning message in correct wording

Signed-off-by: Rong Zhang <i@rong.moe>
---
sound/usb/mixer.c | 54 +++++++++++++++++++++++++++++++++++++++++------
1 file changed, 48 insertions(+), 6 deletions(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index f52ca0d7e6653..7007e0c9489b4 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1664,20 +1664,62 @@ static bool check_insane_volume_range(struct usb_mixer_interface *mixer,
struct snd_kcontrol *kctl,
struct usb_mixer_elem_info *cval)
{
- int range = (cval->max - cval->min) / cval->res;
+ int range, steps, threshold;

/*
- * Are there devices with volume range more than 255? I use a bit more
- * to be sure. 384 is a resolution magic number found on Logitech
- * devices. It will definitively catch all buggy Logitech devices.
+ * If a device quirk has overrode our TLV callback, no warning should
+ * be generated since our checks are only meaningful for dB volume.
*/
- if (range > 384) {
+ if (!(kctl->vd[0].access & SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK) ||
+ kctl->tlv.c != snd_usb_mixer_vol_tlv)
+ return false;
+
+ /*
+ * Meaningless volume control capability (<1dB). This should cover
+ * devices mapping their volume to val = 0/100/1, which are very likely
+ * to be quirky.
+ */
+ range = cval->max - cval->min;
+ if (range < 256) {
usb_audio_warn(mixer->chip,
- "Warning! Unlikely big volume range (=%u), cval->res is probably wrong.",
+ "Warning! Unlikely small volume range (=%u), linear volume or custom curve?",
range);
return true;
}

+ steps = range / cval->res;
+
+ /*
+ * There are definitely devices with ~20,000 ranges (e.g., HyperX Cloud
+ * III with val = -18944/0/1), so we use some heuristics here:
+ *
+ * min < 0 < max: Attenuator + amplifier? Likely to be sane
+ *
+ * min < 0 = max: DSP? Voltage attenuator with FW conversion to dB?
+ * Likely to be sane
+ *
+ * min < max < 0: Measured values? Neutral
+ *
+ * min = 0 < max: Oversimplified FW conversion? Linear volume? Likely to
+ * be quirky (e.g., MV-SILICON)
+ *
+ * 0 < min < max: Amplifier with fixed gains? Likely to be quirky
+ * (e.g., Logitech webcam)
+ */
+ if (cval->min < 0 && 0 <= cval->max)
+ threshold = 24576; /* 65535 * (3 / 8) */
+ else if (cval->min < cval->max && cval->max < 0)
+ threshold = 1024;
+ else
+ threshold = 384;
+
+ if (steps > threshold) {
+ usb_audio_warn(mixer->chip,
+ "Warning! Unlikely big volume step count (=%u), linear volume or wrong cval->res?",
+ steps);
+ return true;
+ }
+
return false;
}

--
2.51.0