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ALSA: snd-meastro3: Document hardware volume control a bit 

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@redhat.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Hans de Goede 2010-04-21 11:04:07 -04:00 committed by Takashi Iwai
parent 6458a54423
commit 20133d4cd3
1 changed files with 18 additions and 4 deletions
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22
sound/pci/maestro3.c
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@ -1598,6 +1598,10 @@ 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;
@ -1609,7 +1613,15 @@ 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);
@ -1629,7 +1641,9 @@ 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);
@ -1638,7 +1652,7 @@ 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)
@ -1650,7 +1664,7 @@ 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)