ALSA: usb-audio - Correct bogus volume dB information

Some USB devices give bogus dB information and it screws up PA.
It's better to detect a broken value and correct it in the driver
before exposing the value to the outside.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 9 insertions, 0 deletions

diff --git a/sound/usb/usbmixer.c b/sound/usb/usbmixer.c
index f127bfd97c07..539b427d08c6 100644
--- a/sound/usb/usbmixer.c
+++ b/sound/usb/usbmixer.c
@@ -470,6 +470,15 @@ static int mixer_vol_tlv(struct snd_kcontrol *kcontrol, int op_flag,
          */
         scale[2] = (convert_signed_value(cval, cval->min) * 100) / 256;
         scale[3] = (convert_signed_value(cval, cval->max) * 100) / 256;
+        if (scale[3] <= scale[2]) {
+                /* something is wrong; assume it's either from/to 0dB */
+                if (scale[2] < 0)
+                        scale[3] = 0;
+                else if (scale[2] > 0)
+                        scale[2] = 0;
+                else /* totally crap, return an error */
+                        return -EINVAL;
+        }
         if (copy_to_user(_tlv, scale, sizeof(scale)))
                 return -EFAULT;
         return 0;