[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: Jaroslav Kysela <perex@perex.cz>

1 files changed, 28 insertions, 9 deletions

diff --git a/sound/pci/intel8x0.c b/sound/pci/intel8x0.c
index 57648810eaf1..c86ff499460b 100644
--- a/sound/pci/intel8x0.c
+++ b/sound/pci/intel8x0.c
@@ -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;