ALSA: via82xx: allow changing the initial DXS volume

As per-stream volume controls, the DXS controls are not intended to
adjust the overall sound level and so are initialized every time
a stream is opened.  However, there are special situations where one
wants to reduce the overall volume in the digital domain, i.e., before
the AC'97 codec's PCM volume control.  To allow this, add a module
parameter that sets the initial DXS volume.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Tested-by: Soeren D. Schulze <soeren.d.schulze@gmx.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/via82xx.c

@@ -85,6 +85,7 @@ static int joystick;
 static int ac97_clock = 48000;
 static char *ac97_quirk;
 static int dxs_support;
+static int dxs_init_volume = 31;
 static int nodelay;
 
 module_param(index, int, 0444);
@@ -103,6 +104,8 @@ module_param(ac97_quirk, charp, 0444);
 MODULE_PARM_DESC(ac97_quirk, "AC'97 workaround for strange hardware.");
 module_param(dxs_support, int, 0444);
 MODULE_PARM_DESC(dxs_support, "Support for DXS channels (0 = auto, 1 = enable, 2 = disable, 3 = 48k only, 4 = no VRA, 5 = enable any sample rate)");
+module_param(dxs_init_volume, int, 0644);
+MODULE_PARM_DESC(dxs_init_volume, "initial DXS volume (0-31)");
 module_param(nodelay, int, 0444);
 MODULE_PARM_DESC(nodelay, "Disable 500ms init delay");
 
@@ -1245,8 +1248,10 @@ static int snd_via8233_playback_open(struct snd_pcm_substream *substream)
 		return err;
 	stream = viadev->reg_offset / 0x10;
 	if (chip->dxs_controls[stream]) {
-		chip->playback_volume[stream][0] = 0;
-		chip->playback_volume[stream][1] = 0;
+		chip->playback_volume[stream][0] =
+				VIA_DXS_MAX_VOLUME - (dxs_init_volume & 31);
+		chip->playback_volume[stream][1] =
+				VIA_DXS_MAX_VOLUME - (dxs_init_volume & 31);
 		chip->dxs_controls[stream]->vd[0].access &=
 			~SNDRV_CTL_ELEM_ACCESS_INACTIVE;
 		snd_ctl_notify(chip->card, SNDRV_CTL_EVENT_MASK_VALUE |