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ALSA: usb-audio: Drop bogus dB range in too low level

Message ID 20210227105737.3656-1-tiwai@suse.de (mailing list archive)
State Accepted
Commit 21cba9c5359dd9d1bffe355336cfec0b66d1ee52
Headers show
Series ALSA: usb-audio: Drop bogus dB range in too low level | expand

Commit Message

Takashi Iwai Feb. 27, 2021, 10:57 a.m. UTC
Some USB audio firmware seem to report broken dB values for the volume
controls, and this screws up applications like PulseAudio who blindly
trusts the given data.  For example, Edifier G2000 reports a PCM
volume from -128dB to -127dB, and this results in barely inaudible

This patch adds a sort of sanity check at parsing the dB values in
USB-audio driver and disables the dB reporting if the range looks
bogus.  Here, we assume -96dB as the bottom line of the max dB.

Note that, if one can figure out that proper dB range later, it can be
patched in the mixer maps.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=211929
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
 sound/usb/mixer.c | 11 +++++++++++
 1 file changed, 11 insertions(+)
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diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index b1c78db0d470..b004b2e63a5d 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1307,6 +1307,17 @@  static int get_min_max_with_quirks(struct usb_mixer_elem_info *cval,
 			/* totally crap, return an error */
 			return -EINVAL;
+	} else {
+		/* if the max volume is too low, it's likely a bogus range;
+		 * here we use -96dB as the threshold
+		 */
+		if (cval->dBmax <= -9600) {
+			usb_audio_info(cval->head.mixer->chip,
+				       "%d:%d: bogus dB values (%d/%d), disabling dB reporting\n",
+				       cval->head.id, mixer_ctrl_intf(cval->head.mixer),
+				       cval->dBmin, cval->dBmax);
+			cval->dBmin = cval->dBmax = 0;
+		}
 	return 0;