[media] em28xx: properly implement AC97 wait code

Instead of assuming that msleep() is precise, use a jiffies
based code to wait for AC97 to be available.
Reviewed-by: NFrank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/em28xx/em28xx-core.c

@@ -23,6 +23,7 @@
  */
 
 #include <linux/init.h>
+#include <linux/jiffies.h>
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/slab.h>
@@ -252,16 +253,18 @@ EXPORT_SYMBOL_GPL(em28xx_toggle_reg_bits);
  */
 static int em28xx_is_ac97_ready(struct em28xx *dev)
 {
-	int ret, i;
+	unsigned long timeout = jiffies + msecs_to_jiffies(EM28XX_AC97_XFER_TIMEOUT);
+	int ret;
 
 	/* Wait up to 50 ms for AC97 command to complete */
-	for (i = 0; i < 10; i++, msleep(5)) {
+	while (time_is_after_jiffies(timeout)) {
 		ret = em28xx_read_reg(dev, EM28XX_R43_AC97BUSY);
 		if (ret < 0)
 			return ret;
 
 		if (!(ret & 0x01))
 			return 0;
+		msleep(5);
 	}
 
 	em28xx_warn("AC97 command still being executed: not handled properly!\n");

drivers/media/usb/em28xx/em28xx.h

@@ -186,6 +186,9 @@
 /* time in msecs to wait for i2c writes to finish */
 #define EM2800_I2C_XFER_TIMEOUT		20
 
+/* time in msecs to wait for AC97 xfers to finish */
+#define EM28XX_AC97_XFER_TIMEOUT	100
+
 /* max. number of button state polling addresses */
 #define EM28XX_NUM_BUTTON_ADDRESSES_MAX		5