ALSA: usb-audio - Add volume range check and warn if it too big

Signed-off-by: Alexey Fisher <bug-track@fisher-privat.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 16 insertions, 0 deletions

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 7df89b3d7de..3e3116c5bc5 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -987,6 +987,7 @@ static void build_feature_ctl(struct mixer_build *state, void *raw_desc,
         struct snd_kcontrol *kctl;
         struct usb_mixer_elem_info *cval;
         const struct usbmix_name_map *map;
+        unsigned int range;
 
         control++; /* change from zero-based to 1-based value */
 
@@ -1136,6 +1137,21 @@ static void build_feature_ctl(struct mixer_build *state, void *raw_desc,
 
         }
 
+        range = (cval->max - cval->min) / cval->res;
+        /* 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 (range > 384) {
+                snd_printk(KERN_WARNING "usb_audio: Warning! Unlikely big "
+                           "volume range (=%u), cval->res is probably wrong.",
+                           range);
+                snd_printk(KERN_WARNING "usb_audio: [%d] FU [%s] ch = %d, "
+                           "val = %d/%d/%d", cval->id,
+                           kctl->id.name, cval->channels,
+                           cval->min, cval->max, cval->res);
+        }
+
         snd_printdd(KERN_INFO "[%d] FU [%s] ch = %d, val = %d/%d/%d\n",
                     cval->id, kctl->id.name, cval->channels, cval->min, cval->max, cval->res);
         add_control_to_empty(state, kctl);