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Commit 4f550df5 authored by Karsten Wiese's avatar Karsten Wiese Committed by Jaroslav Kysela
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[ALSA] Reduce interrupt latency in sound/pci/via82xx.c 



Modules: VIA82xx driver

The change only affects the via823x kind of chips.
Here the  via8233_pcm_pointer_hw() function
(named snd_via8233_pcm_pointer() before)
needed to loop until a non zero position is red from the chip.

Measurements have shown that more than 200 loops are typically needed on
an Athlon64.
As io-reads cost many cycles, those loops sum up huge.
via8233_pcm_pointer_hw() runs either in interrupt or with interrupts
disabled. So it introduces significant interrupt latency.

The patch introduces a calculated position value hwptr_done,
that is updated by the interrupt routine when a period is completed.
It is only used, if the 823x chip returns a zero position, which can't
be interpreted reliably.

Further optimisation is applied on the 8233 chip's interrupt routine:
Only the SGD_SHADOW is read, as it contains all infos needed.
We ommit ~5 more register reads that way.

Signed-off-by: default avatarKarsten Wiese <annabellesgarden@yahoo.de>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent f0597a41

sound/pci/via82xx.c

+131 −39
Original line number Diff line number Diff line
@@ -41,6 +41,9 @@ 
 *	  device for applications.

 *	- clean up the code, separate low-level initialization

 *	  routines for each chipset.

 *

 * Sep. 26, 2005	Karsten Wiese <annabellesgarden@yahoo.de>

 *	- Optimize position calculation for the 823x chips. 

 */



#include <sound/driver.h>
@@ -131,6 +134,7 @@ module_param(enable, int, 0444); 
/* common offsets */

#define VIA_REG_OFFSET_STATUS		0x00	/* byte - channel status */

#define   VIA_REG_STAT_ACTIVE		0x80	/* RO */

#define   VIA8233_SHADOW_STAT_ACTIVE	0x08	/* RO */

#define   VIA_REG_STAT_PAUSED		0x40	/* RO */

#define   VIA_REG_STAT_TRIGGER_QUEUED	0x08	/* RO */

#define   VIA_REG_STAT_STOPPED		0x04	/* RWC */
@@ -329,6 +333,9 @@ struct via_dev { 
	unsigned int fragsize;

	unsigned int bufsize;

	unsigned int bufsize2;

	int hwptr_done;		/* processed frame position in the buffer */

	int in_interrupt;

	int shadow_shift;

};
@@ -395,8 +402,10 @@ struct _snd_via82xx { 
};



static struct pci_device_id snd_via82xx_ids[] = {

	{ 0x1106, 0x3058, PCI_ANY_ID, PCI_ANY_ID, 0, 0, TYPE_CARD_VIA686, },	/* 686A */

	{ 0x1106, 0x3059, PCI_ANY_ID, PCI_ANY_ID, 0, 0, TYPE_CARD_VIA8233, },	/* VT8233 */

	/* 0x1106, 0x3058 */

	{ PCI_VENDOR_ID_VIA, PCI_DEVICE_ID_VIA_82C686_5, PCI_ANY_ID, PCI_ANY_ID, 0, 0, TYPE_CARD_VIA686, },	/* 686A */

	/* 0x1106, 0x3059 */

	{ PCI_VENDOR_ID_VIA, PCI_DEVICE_ID_VIA_8233_5, PCI_ANY_ID, PCI_ANY_ID, 0, 0, TYPE_CARD_VIA8233, },	/* VT8233 */

	{ 0, }

};
@@ -598,14 +607,15 @@ static void snd_via82xx_channel_reset(via82xx_t *chip, viadev_t *viadev) 
	outb(0x00, VIADEV_REG(viadev, OFFSET_TYPE)); /* for via686 */

	// outl(0, VIADEV_REG(viadev, OFFSET_CURR_PTR));

	viadev->lastpos = 0;

	viadev->hwptr_done = 0;

}





/*

 *  Interrupt handler

 *  Used for 686 and 8233A

 */



static irqreturn_t snd_via82xx_interrupt(int irq, void *dev_id, struct pt_regs *regs)

static irqreturn_t snd_via686_interrupt(int irq, void *dev_id, struct pt_regs *regs)

{

	via82xx_t *chip = dev_id;

	unsigned int status;
@@ -624,13 +634,23 @@ static irqreturn_t snd_via82xx_interrupt(int irq, void *dev_id, struct pt_regs * 
	for (i = 0; i < chip->num_devs; i++) {

		viadev_t *viadev = &chip->devs[i];

		unsigned char c_status = inb(VIADEV_REG(viadev, OFFSET_STATUS));

		c_status &= (VIA_REG_STAT_EOL|VIA_REG_STAT_FLAG|VIA_REG_STAT_STOPPED);

		if (! c_status)

		if (! (c_status & (VIA_REG_STAT_EOL|VIA_REG_STAT_FLAG|VIA_REG_STAT_STOPPED)))

			continue;

		if (viadev->substream && viadev->running) {

			/*

			 * Update hwptr_done based on 'period elapsed'

			 * interrupts. We'll use it, when the chip returns 0 

			 * for OFFSET_CURR_COUNT.

			 */

			if (c_status & VIA_REG_STAT_EOL)

				viadev->hwptr_done = 0;

			else

				viadev->hwptr_done += viadev->fragsize;

			viadev->in_interrupt = c_status;

			spin_unlock(&chip->reg_lock);

			snd_pcm_period_elapsed(viadev->substream);

			spin_lock(&chip->reg_lock);

			viadev->in_interrupt = 0;

		}

		outb(c_status, VIADEV_REG(viadev, OFFSET_STATUS)); /* ack */

	}
@@ -638,6 +658,60 @@ static irqreturn_t snd_via82xx_interrupt(int irq, void *dev_id, struct pt_regs * 
	return IRQ_HANDLED;

}



/*

 *  Interrupt handler

 */

static irqreturn_t snd_via8233_interrupt(int irq, void *dev_id, struct pt_regs *regs)

{

	via82xx_t *chip = dev_id;

	unsigned int status;

	unsigned int i;

	int irqreturn = 0;



	/* check status for each stream */

	spin_lock(&chip->reg_lock);

	status = inl(VIAREG(chip, SGD_SHADOW));



	for (i = 0; i < chip->num_devs; i++) {

		viadev_t *viadev = &chip->devs[i];

		snd_pcm_substream_t *substream;

		unsigned char c_status, shadow_status;



		shadow_status = (status >> viadev->shadow_shift) &

			(VIA8233_SHADOW_STAT_ACTIVE|VIA_REG_STAT_EOL|

			 VIA_REG_STAT_FLAG);

		c_status = shadow_status & (VIA_REG_STAT_EOL|VIA_REG_STAT_FLAG);

		if (!c_status)

			continue;



		substream = viadev->substream;

		if (substream && viadev->running) {

			/*

			 * Update hwptr_done based on 'period elapsed'

			 * interrupts. We'll use it, when the chip returns 0 

			 * for OFFSET_CURR_COUNT.

			 */

			if (c_status & VIA_REG_STAT_EOL)

				viadev->hwptr_done = 0;

			else

				viadev->hwptr_done += viadev->fragsize;

			viadev->in_interrupt = c_status;

			if (shadow_status & VIA8233_SHADOW_STAT_ACTIVE)

				viadev->in_interrupt |= VIA_REG_STAT_ACTIVE;

			spin_unlock(&chip->reg_lock);



			snd_pcm_period_elapsed(substream);



			spin_lock(&chip->reg_lock);

			viadev->in_interrupt = 0;

		}

		outb(c_status, VIADEV_REG(viadev, OFFSET_STATUS)); /* ack */

		irqreturn = 1;

	}

	spin_unlock(&chip->reg_lock);

	return IRQ_RETVAL(irqreturn);

}



/*

 *  PCM callbacks

 */
@@ -701,6 +775,8 @@ static inline unsigned int calc_linear_pos(viadev_t *viadev, unsigned int idx, u 
	size = viadev->idx_table[idx].size;

	base = viadev->idx_table[idx].offset;

	res = base + size - count;

	if (res >= viadev->bufsize)

		res -= viadev->bufsize;



	/* check the validity of the calculated position */

	if (size < count) {
@@ -730,9 +806,6 @@ static inline unsigned int calc_linear_pos(viadev_t *viadev, unsigned int idx, u 
			}

		}

	}

	viadev->lastpos = res; /* remember the last position */

	if (res >= viadev->bufsize)

		res -= viadev->bufsize;

	return res;

}
@@ -760,6 +833,7 @@ static snd_pcm_uframes_t snd_via686_pcm_pointer(snd_pcm_substream_t *substream) 
	else /* CURR_PTR holds the address + 8 */

		idx = ((ptr - (unsigned int)viadev->table.addr) / 8 - 1) % viadev->tbl_entries;

	res = calc_linear_pos(viadev, idx, count);

	viadev->lastpos = res; /* remember the last position */

	spin_unlock(&chip->reg_lock);



	return bytes_to_frames(substream->runtime, res);
@@ -773,20 +847,21 @@ static snd_pcm_uframes_t snd_via8233_pcm_pointer(snd_pcm_substream_t *substream) 
	via82xx_t *chip = snd_pcm_substream_chip(substream);

	viadev_t *viadev = (viadev_t *)substream->runtime->private_data;

	unsigned int idx, count, res;

	int timeout = 5000;

	int status;

	

	snd_assert(viadev->tbl_entries, return 0);

	if (!(inb(VIADEV_REG(viadev, OFFSET_STATUS)) & VIA_REG_STAT_ACTIVE))

		return 0;



	spin_lock(&chip->reg_lock);

	do {

	count = inl(VIADEV_REG(viadev, OFFSET_CURR_COUNT));

		/* some mobos read 0 count */

		if ((count & 0xffffff) || ! viadev->running)

			break;

	} while (--timeout);

	if (! timeout)

		snd_printd(KERN_ERR "zero position is read\n");

	status = viadev->in_interrupt;

	if (!status)

		status = inb(VIADEV_REG(viadev, OFFSET_STATUS));



	if (!(status & VIA_REG_STAT_ACTIVE)) {

		res = 0;

		goto unlock;

	}

	if (count & 0xffffff) {

		idx = count >> 24;

		if (idx >= viadev->tbl_entries) {

#ifdef POINTER_DEBUG
@@ -797,6 +872,19 @@ static snd_pcm_uframes_t snd_via8233_pcm_pointer(snd_pcm_substream_t *substream) 
			count &= 0xffffff;

			res = calc_linear_pos(viadev, idx, count);

		}

	} else {

		res = viadev->hwptr_done;

		if (!viadev->in_interrupt) {

			if (status & VIA_REG_STAT_EOL) {

				res = 0;

			} else

				if (status & VIA_REG_STAT_FLAG) {

					res += viadev->fragsize;

				}

		}

	}			    

unlock:

	viadev->lastpos = res;

	spin_unlock(&chip->reg_lock);



	return bytes_to_frames(substream->runtime, res);
@@ -1241,9 +1329,10 @@ static snd_pcm_ops_t snd_via8233_capture_ops = { 
};





static void init_viadev(via82xx_t *chip, int idx, unsigned int reg_offset, int direction)

static void init_viadev(via82xx_t *chip, int idx, unsigned int reg_offset, int shadow_pos, int direction)

{

	chip->devs[idx].reg_offset = reg_offset;

	chip->devs[idx].shadow_shift = shadow_pos * 4;

	chip->devs[idx].direction = direction;

	chip->devs[idx].port = chip->port + reg_offset;

}
@@ -1273,9 +1362,9 @@ static int __devinit snd_via8233_pcm_new(via82xx_t *chip) 
	chip->pcms[0] = pcm;

	/* set up playbacks */

	for (i = 0; i < 4; i++)

		init_viadev(chip, i, 0x10 * i, 0);

		init_viadev(chip, i, 0x10 * i, i, 0);

	/* capture */

	init_viadev(chip, chip->capture_devno, VIA_REG_CAPTURE_8233_STATUS, 1);

	init_viadev(chip, chip->capture_devno, VIA_REG_CAPTURE_8233_STATUS, 6, 1);



	if ((err = snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV_SG,

							 snd_dma_pci_data(chip->pci), 64*1024, 128*1024)) < 0)
@@ -1291,9 +1380,9 @@ static int __devinit snd_via8233_pcm_new(via82xx_t *chip) 
	strcpy(pcm->name, chip->card->shortname);

	chip->pcms[1] = pcm;

	/* set up playback */

	init_viadev(chip, chip->multi_devno, VIA_REG_MULTPLAY_STATUS, 0);

	init_viadev(chip, chip->multi_devno, VIA_REG_MULTPLAY_STATUS, 4, 0);

	/* set up capture */

	init_viadev(chip, chip->capture_devno + 1, VIA_REG_CAPTURE_8233_STATUS + 0x10, 1);

	init_viadev(chip, chip->capture_devno + 1, VIA_REG_CAPTURE_8233_STATUS + 0x10, 7, 1);



	if ((err = snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV_SG,

						         snd_dma_pci_data(chip->pci), 64*1024, 128*1024)) < 0)
@@ -1326,9 +1415,9 @@ static int __devinit snd_via8233a_pcm_new(via82xx_t *chip) 
	strcpy(pcm->name, chip->card->shortname);

	chip->pcms[0] = pcm;

	/* set up playback */

	init_viadev(chip, chip->multi_devno, VIA_REG_MULTPLAY_STATUS, 0);

	init_viadev(chip, chip->multi_devno, VIA_REG_MULTPLAY_STATUS, 4, 0);

	/* capture */

	init_viadev(chip, chip->capture_devno, VIA_REG_CAPTURE_8233_STATUS, 1);

	init_viadev(chip, chip->capture_devno, VIA_REG_CAPTURE_8233_STATUS, 6, 1);



	if ((err = snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV_SG,

							 snd_dma_pci_data(chip->pci), 64*1024, 128*1024)) < 0)
@@ -1347,7 +1436,7 @@ static int __devinit snd_via8233a_pcm_new(via82xx_t *chip) 
	strcpy(pcm->name, chip->card->shortname);

	chip->pcms[1] = pcm;

	/* set up playback */

	init_viadev(chip, chip->playback_devno, 0x30, 0);

	init_viadev(chip, chip->playback_devno, 0x30, 3, 0);



	if ((err = snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV_SG,

							 snd_dma_pci_data(chip->pci), 64*1024, 128*1024)) < 0)
@@ -1377,8 +1466,8 @@ static int __devinit snd_via686_pcm_new(via82xx_t *chip) 
	pcm->private_data = chip;

	strcpy(pcm->name, chip->card->shortname);

	chip->pcms[0] = pcm;

	init_viadev(chip, 0, VIA_REG_PLAYBACK_STATUS, 0);

	init_viadev(chip, 1, VIA_REG_CAPTURE_STATUS, 1);

	init_viadev(chip, 0, VIA_REG_PLAYBACK_STATUS, 0, 0);

	init_viadev(chip, 1, VIA_REG_CAPTURE_STATUS, 0, 1);



	if ((err = snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV_SG,

							 snd_dma_pci_data(chip->pci), 64*1024, 128*1024)) < 0)
@@ -2134,7 +2223,10 @@ static int __devinit snd_via82xx_create(snd_card_t * card, 
		return err;

	}

	chip->port = pci_resource_start(pci, 0);

	if (request_irq(pci->irq, snd_via82xx_interrupt, SA_INTERRUPT|SA_SHIRQ,

	if (request_irq(pci->irq,

			chip_type == TYPE_VIA8233 ?

			snd_via8233_interrupt :	snd_via686_interrupt,

			SA_INTERRUPT|SA_SHIRQ,

			card->driver, (void *)chip)) {

		snd_printk("unable to grab IRQ %d\n", pci->irq);

		snd_via82xx_free(chip);