[PATCH v3 4/4] stk1160: Give the chip some time to retrieve data from AC97 codec.

[Marcel Hasler <mahasler@gmail.com>]

The STK1160 needs some time to transfer data from the AC97 registers into its own. On some
systems reading the chip's own registers to soon will return wrong values. The "proper" way to
handle this would be to poll STK1160_AC97CTL_0 after every read or write command until the
command bit has been cleared, but this may not be worth the hassle.

Signed-off-by: Marcel Hasler <mahasler@gmail.com>
---
 drivers/media/usb/stk1160/stk1160-ac97.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/media/usb/stk1160/stk1160-ac97.c b/drivers/media/usb/stk1160/stk1160-ac97.c
index 60327af..b39f51b 100644
--- a/drivers/media/usb/stk1160/stk1160-ac97.c
+++ b/drivers/media/usb/stk1160/stk1160-ac97.c
@@ -23,6 +23,7 @@
  *
  */
 
+#include <linux/delay.h>
 #include <linux/module.h>
 
 #include "stk1160.h"
@@ -64,6 +65,14 @@ static u16 stk1160_read_ac97(struct stk1160 *dev, u16 reg)
 	 */
 	stk1160_write_reg(dev, STK1160_AC97CTL_0, 0x8b);
 
+	/*
+	 * Give the chip some time to transfer the data.
+	 * The proper way would be to poll STK1160_AC97CTL_0
+	 * until the command bit has been cleared, but this
+	 * may not be worth the hassle.
+	 */
+	usleep_range(20, 40);
+
 	/* Retrieve register value */
 	stk1160_read_reg(dev, STK1160_AC97_CMD, &vall);
 	stk1160_read_reg(dev, STK1160_AC97_CMD + 1, &valh);
-- 
2.10.2