ALSA: hda - Add sanity check of vmaster slave dB steps

Check whether all vmaster slaves have the same dB steps.  Otherwise
the behavior would become inconsistent.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/hda_codec.c

@@ -2661,7 +2661,7 @@ static int check_slave_present(void *data, struct snd_kcontrol *sctl)
 }
 
 /* guess the value corresponding to 0dB */
-static int get_kctl_0dB_offset(struct snd_kcontrol *kctl)
+static int get_kctl_0dB_offset(struct snd_kcontrol *kctl, int *step_to_check)
 {
 	int _tlv[4];
 	const int *tlv = NULL;
@@ -2681,6 +2681,12 @@ static int get_kctl_0dB_offset(struct snd_kcontrol *kctl)
 		step &= ~TLV_DB_SCALE_MUTE;
 		if (!step)
 			return -1;
+		if (*step_to_check && *step_to_check != step) {
+			snd_printk(KERN_ERR "hda_codec: Mismatching dB step for vmaster slave (%d!=%d)\n",
+				   *step_to_check, step);
+			return -1;
+		}
+		*step_to_check = step;
 		val = -tlv[2] / step;
 	}
 	return val;
@@ -2703,7 +2709,7 @@ static int put_kctl_with_value(struct snd_kcontrol *kctl, int val)
 /* initialize the slave volume with 0dB */
 static int init_slave_0dB(void *data, struct snd_kcontrol *slave)
 {
-	int offset = get_kctl_0dB_offset(slave);
+	int offset = get_kctl_0dB_offset(slave, data);
 	if (offset > 0)
 		put_kctl_with_value(slave, offset);
 	return 0;
@@ -2764,9 +2770,11 @@ int __snd_hda_add_vmaster(struct hda_codec *codec, char *name,
 
 	/* init with master mute & zero volume */
 	put_kctl_with_value(kctl, 0);
-	if (init_slave_vol)
+	if (init_slave_vol) {
+		int step = 0;
 		map_slaves(codec, slaves, suffix,
-			   tlv ? init_slave_0dB : init_slave_unmute, kctl);
+			   tlv ? init_slave_0dB : init_slave_unmute, &step);
+	}
 
 	if (ctl_ret)
 		*ctl_ret = kctl;