[ALSA] ac97: Fix volume control bit size detection for STAC9704.

AC97 Codec

Signed-off-by: James Courtier-Dutton <James@superbug.co.uk>

1 files changed, 5 insertions, 0 deletions

diff --git a/sound/pci/ac97/ac97_codec.c b/sound/pci/ac97/ac97_codec.c
index 94cd989cff20..1f09653dc0f3 100644
--- a/sound/pci/ac97/ac97_codec.c
+++ b/sound/pci/ac97/ac97_codec.c
@@ -1078,6 +1078,11 @@ static void check_volume_resolution(ac97_t *ac97, int reg, unsigned char *lo_max
         for (i = 0 ; i < ARRAY_SIZE(cbit); i++) {
                 unsigned short val;
                 snd_ac97_write(ac97, reg, 0x8080 | cbit[i] | (cbit[i] << 8));
+                /* Do the read twice due to buffers on some ac97 codecs.
+                 * e.g. The STAC9704 returns exactly what you wrote the the register
+                 * if you read it immediately. This causes the detect routine to fail.
+                 */
+                val = snd_ac97_read(ac97, reg);
                 val = snd_ac97_read(ac97, reg);
                 if (! *lo_max && (val & 0x7f) == cbit[i])
                         *lo_max = max[i];