sound: ymfpci: increase timer resolution to 96 kHz

Allow the interval timer to be programmed with its full 96 kHz
precision.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/ymfpci.h

@@ -331,6 +331,7 @@ struct snd_ymfpci {
 	struct snd_ac97 *ac97;
 	struct snd_rawmidi *rawmidi;
 	struct snd_timer *timer;
+	unsigned int timer_ticks;
 
 	struct pci_dev *pci;
 	struct snd_card *card;

sound/pci/ymfpci/ymfpci_main.c

@@ -834,7 +834,7 @@ static irqreturn_t snd_ymfpci_interrupt(int irq, void *dev_id)
 	status = snd_ymfpci_readw(chip, YDSXGR_INTFLAG);
 	if (status & 1) {
 		if (chip->timer)
-			snd_timer_interrupt(chip->timer, chip->timer->sticks);
+			snd_timer_interrupt(chip->timer, chip->timer_ticks);
 	}
 	snd_ymfpci_writew(chip, YDSXGR_INTFLAG, status);
 
@@ -1885,8 +1885,18 @@ static int snd_ymfpci_timer_start(struct snd_timer *timer)
 	unsigned int count;
 
 	chip = snd_timer_chip(timer);
-	count = (timer->sticks << 1) - 1;
 	spin_lock_irqsave(&chip->reg_lock, flags);
+	if (timer->sticks > 1) {
+		chip->timer_ticks = timer->sticks;
+		count = timer->sticks - 1;
+	} else {
+		/*
+		 * Divisor 1 is not allowed; fake it by using divisor 2 and
+		 * counting two ticks for each interrupt.
+		 */
+		chip->timer_ticks = 2;
+		count = 2 - 1;
+	}
 	snd_ymfpci_writew(chip, YDSXGR_TIMERCOUNT, count);
 	snd_ymfpci_writeb(chip, YDSXGR_TIMERCTRL, 0x03);
 	spin_unlock_irqrestore(&chip->reg_lock, flags);
@@ -1909,14 +1919,14 @@ static int snd_ymfpci_timer_precise_resolution(struct snd_timer *timer,
 					       unsigned long *num, unsigned long *den)
 {
 	*num = 1;
-	*den = 48000;
+	*den = 96000;
 	return 0;
 }
 
 static struct snd_timer_hardware snd_ymfpci_timer_hw = {
 	.flags = SNDRV_TIMER_HW_AUTO,
-	.resolution = 20833, /* 1/fs = 20.8333...us */
-	.ticks = 0x8000,
+	.resolution = 10417, /* 1 / 96 kHz = 10.41666...us */
+	.ticks = 0x10000,
 	.start = snd_ymfpci_timer_start,
 	.stop = snd_ymfpci_timer_stop,
 	.precise_resolution = snd_ymfpci_timer_precise_resolution,