[alsa-devel] [PATCH 2/3] snd-meastro3: Document hardware volume control a bit
Hans de Goede
hdegoede at redhat.com
Wed Apr 21 14:15:27 CEST 2010
While working on a fix for the volume being muted on the allegro in my
Compaq EVO N600C after suspend, I've learned a few things about the hardware
volume control worth documenting. The actual fix for the suspend / resume
issue is in the next patch in this set.
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
sound/pci/maestro3.c | 22 ++++++++++++++++++----
1 files changed, 18 insertions(+), 4 deletions(-)
diff --git a/sound/pci/maestro3.c b/sound/pci/maestro3.c
index 491a2fc..c6593cf 100644
--- a/sound/pci/maestro3.c
+++ b/sound/pci/maestro3.c
@@ -1597,6 +1597,10 @@ static void snd_m3_update_ptr(struct snd_m3 *chip, struct m3_dma *s)
}
}
+/* The m3's hardware volume works by incrementing / decrementing 2 counters
+ (without wrap around) in response to volume button presses and then
+ generating an interrupt. The pair of counters is stored in bits 1-3 and 5-7
+ of a byte wide register. The meaning of bits 0 and 4 is unknown. */
static void snd_m3_update_hw_volume(unsigned long private_data)
{
struct snd_m3 *chip = (struct snd_m3 *) private_data;
@@ -1608,7 +1612,15 @@ static void snd_m3_update_hw_volume(unsigned long private_data)
values. */
x = inb(chip->iobase + SHADOW_MIX_REG_VOICE) & 0xee;
- /* Reset the volume control registers. */
+ /* Reset the volume counters to 4. Tests on the allegro integrated
+ into a Compaq N600C laptop, have revealed that:
+ 1) Writing any value will result in the 2 counters being reset to
+ 4 so writing 0x88 is not strictly necessary
+ 2) Writing to any of the 4 involved registers will reset all 4
+ of them (and reading them always returns the same value for all
+ of them)
+ It could be that a maestro deviates from this, so leave the code
+ as is. */
outb(0x88, chip->iobase + SHADOW_MIX_REG_VOICE);
outb(0x88, chip->iobase + HW_VOL_COUNTER_VOICE);
outb(0x88, chip->iobase + SHADOW_MIX_REG_MASTER);
@@ -1623,7 +1635,9 @@ static void snd_m3_update_hw_volume(unsigned long private_data)
val = chip->ac97->regs[AC97_MASTER_VOL];
switch (x) {
case 0x88:
- /* mute */
+ /* The counters have not changed, yet we've received a HV
+ interrupt. According to tests run by various people this
+ happens when pressing the mute button. */
val ^= 0x8000;
chip->ac97->regs[AC97_MASTER_VOL] = val;
outw(val, chip->iobase + CODEC_DATA);
@@ -1632,7 +1646,7 @@ static void snd_m3_update_hw_volume(unsigned long private_data)
&chip->master_switch->id);
break;
case 0xaa:
- /* volume up */
+ /* counters increased by 1 -> volume up */
if ((val & 0x7f) > 0)
val--;
if ((val & 0x7f00) > 0)
@@ -1644,7 +1658,7 @@ static void snd_m3_update_hw_volume(unsigned long private_data)
&chip->master_volume->id);
break;
case 0x66:
- /* volume down */
+ /* counters decreased by 1 -> volume down */
if ((val & 0x7f) < 0x1f)
val++;
if ((val & 0x7f00) < 0x1f00)
--
1.7.0.1
--
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