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Commit 920e4ae3 authored by Jaroslav Kysela's avatar Jaroslav Kysela
Browse files

[ALSA] intel8x0: an attempt to make ac97_clock measurement more reliable 



- use monotonic posix clock to measure time
- try to avoid reading zero from PICB (position in current buffer) register
- show also measured samples
- when clock is near 41000 or 44100, use exactly these values
  (they appears to be reference clocks for hardware manufacturers)

Signed-off-by: default avatarJaroslav Kysela <perex@perex.cz>
parent bbf6ad13

sound/pci/intel8x0.c

+28 −9
Original line number Diff line number Diff line
@@ -2661,8 +2661,9 @@ static void __devinit intel8x0_measure_ac97_clock(struct intel8x0 *chip) 
	struct snd_pcm_substream *subs;

	struct ichdev *ichdev;

	unsigned long port;

	unsigned long pos, t;

	struct timeval start_time, stop_time;

	unsigned long pos, pos1, t;

	int civ, timeout = 1000;

	struct timespec start_time, stop_time;



	if (chip->ac97_bus->clock != 48000)

		return; /* specified in module option */
@@ -2693,16 +2694,27 @@ static void __devinit intel8x0_measure_ac97_clock(struct intel8x0 *chip) 
		iputbyte(chip, port + ICH_REG_OFF_CR, ICH_IOCE);

		iputdword(chip, ICHREG(ALI_DMACR), 1 << ichdev->ali_slot);

	}

	do_gettimeofday(&start_time);

	do_posix_clock_monotonic_gettime(&start_time);

	spin_unlock_irq(&chip->reg_lock);

	msleep(50);

	spin_lock_irq(&chip->reg_lock);

	/* check the position */

	do {

		civ = igetbyte(chip, ichdev->reg_offset + ICH_REG_OFF_CIV);

		pos1 = igetword(chip, ichdev->reg_offset + ichdev->roff_picb);

		if (pos1 == 0) {

			udelay(10);

			continue;

		}

		if (civ == igetbyte(chip, ichdev->reg_offset + ICH_REG_OFF_CIV) &&

		    pos1 == igetword(chip, ichdev->reg_offset + ichdev->roff_picb))

			break;

	} while (timeout--);

	pos = ichdev->fragsize1;

	pos -= igetword(chip, ichdev->reg_offset + ichdev->roff_picb) << ichdev->pos_shift;

	pos -= pos1 << ichdev->pos_shift;

	pos += ichdev->position;

	chip->in_measurement = 0;

	do_gettimeofday(&stop_time);

	do_posix_clock_monotonic_gettime(&stop_time);

	/* stop */

	if (chip->device_type == DEVICE_ALI) {

		iputdword(chip, ICHREG(ALI_DMACR), 1 << (ichdev->ali_slot + 16));
@@ -2717,19 +2729,26 @@ static void __devinit intel8x0_measure_ac97_clock(struct intel8x0 *chip) 
	iputbyte(chip, port + ICH_REG_OFF_CR, ICH_RESETREGS);

	spin_unlock_irq(&chip->reg_lock);



	pos /= 4;

	t = stop_time.tv_sec - start_time.tv_sec;

	t *= 1000000;

	t += stop_time.tv_usec - start_time.tv_usec;

	printk(KERN_INFO "%s: measured %lu usecs\n", __func__, t);

	t += (stop_time.tv_nsec - start_time.tv_nsec) / 1000;

	printk(KERN_INFO "%s: measured %lu usecs (%lu samples)\n", __func__, t, pos);

	if (t == 0) {

		snd_printk(KERN_ERR "?? calculation error..\n");

		snd_printk(KERN_ERR "intel8x0: ?? calculation error..\n");

		return;

	}

	pos = (pos / 4) * 1000;

	pos *= 1000;

	pos = (pos / t) * 1000 + ((pos % t) * 1000) / t;

	if (pos < 40000 || pos >= 60000) 

		/* abnormal value. hw problem? */

		printk(KERN_INFO "intel8x0: measured clock %ld rejected\n", pos);

	else if (pos > 40500 || pos < 41500)

		/* first exception - 41000Hz reference clock */

		chip->ac97_bus->clock = 41000;

	else if (pos > 43600 || pos < 44600)

		/* second exception - 44100HZ reference clock */

		chip->ac97_bus->clock = 44100;

	else if (pos < 47500 || pos > 48500)

		/* not 48000Hz, tuning the clock.. */

		chip->ac97_bus->clock = (chip->ac97_bus->clock * 48000) / pos;