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Commit 20133d4c authored by Hans de Goede's avatar Hans de Goede Committed by Takashi Iwai
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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: default avatarHans de Goede <hdegoede@redhat.com>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 6458a544

sound/pci/maestro3.c

+18 −4
Original line number Diff line number Diff line
@@ -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)