[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: Karsten Wiese <annabellesgarden@yahoo.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 131 insertions, 39 deletions

diff --git a/sound/pci/via82xx.c b/sound/pci/via82xx.c
index 7d46bee828c7..eb35b446235c 100644
--- a/sound/pci/via82xx.c
+++ b/sound/pci/via82xx.c
@@ -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, }
 };
 
@@ -550,7 +559,7 @@ static void snd_via82xx_codec_write(ac97_t *ac97,
 {
         via82xx_t *chip = ac97->private_data;
         unsigned int xval;
-        
+
         xval = !ac97->num ? VIA_REG_AC97_CODEC_ID_PRIMARY : VIA_REG_AC97_CODEC_ID_SECONDARY;
         xval <<= VIA_REG_AC97_CODEC_ID_SHIFT;
         xval |= reg << VIA_REG_AC97_CMD_SHIFT;
@@ -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 */
         }
@@ -639,6 +659,60 @@ static irqreturn_t snd_via82xx_interrupt(int irq, void *dev_id, struct pt_regs *
 }
 
 /*
+ *  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);
@@ -773,30 +847,44 @@ 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");
-        idx = count >> 24;
-        if (idx >= viadev->tbl_entries) {
+        count = inl(VIADEV_REG(viadev, OFFSET_CURR_COUNT));
+        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
-                printk("fail: invalid idx = %i/%i\n", idx, viadev->tbl_entries);
+                        printk("fail: invalid idx = %i/%i\n", idx, viadev->tbl_entries);
 #endif
-                res = viadev->lastpos;
+                        res = viadev->lastpos;
+                } else {
+                        count &= 0xffffff;
+                        res = calc_linear_pos(viadev, idx, count);
+                }
         } else {
-                count &= 0xffffff;
-                res = calc_linear_pos(viadev, idx, count);
-        }
+                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);