hw/ac97: Mask out unused bits of volume controls

The Linux ac97 drivers does a number of register read/write tests to
see how much resolution a volume control actually has.

This patch takes this into account by masking out any bits written to
a volume control reg which should not be there according to the spec.

After this the Linux ac97 driver correctly uses a range of 0 - 0x1f for
the PCM out volume, as stated in the spec, and we can fix the FIXME
in update_combined_volume_out().

This patch was also tested with a Windows XP guest without any issues.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: malc <av1474@comtv.ru>

1 files changed, 15 insertions, 5 deletions

diff --git a/hw/ac97.c b/hw/ac97.c
index d175870798..b009257434 100644
--- a/hw/ac97.c
+++ b/hw/ac97.c
@@ -458,8 +458,7 @@ static void update_combined_volume_out (AC97LinkState *s)
 
     get_volume (mixer_load (s, AC97_Master_Volume_Mute), 0x3f, 1,
                 &mute, &lvol, &rvol);
-    /* FIXME: should be 1f according to spec */
-    get_volume (mixer_load (s, AC97_PCM_Out_Volume_Mute), 0x3f, 1,
+    get_volume (mixer_load (s, AC97_PCM_Out_Volume_Mute), 0x1f, 1,
                 &pmute, &plvol, &prvol);
 
     mute = mute | pmute;
@@ -482,11 +481,22 @@ static void update_volume_in (AC97LinkState *s)
 
 static void set_volume (AC97LinkState *s, int index, uint32_t val)
 {
-    mixer_store (s, index, val);
-    if (index == AC97_Master_Volume_Mute || index == AC97_PCM_Out_Volume_Mute) {
+    switch (index) {
+    case AC97_Master_Volume_Mute:
+        val &= 0xbf3f;
+        mixer_store (s, index, val);
         update_combined_volume_out (s);
-    } else if (index == AC97_Record_Gain_Mute) {
+        break;
+    case AC97_PCM_Out_Volume_Mute:
+        val &= 0x9f1f;
+        mixer_store (s, index, val);
+        update_combined_volume_out (s);
+        break;
+    case AC97_Record_Gain_Mute:
+        val &= 0x8f0f;
+        mixer_store (s, index, val);
         update_volume_in (s);
+        break;
     }
 }