[media] stk1160: Wait for completion of transfers to and from AC97 codec

The STK1160 needs some time to transfer data to and from the AC97 codec.
The transfer completion is indicated by command read/write bits in the
chip's audio control register. The driver should poll these bits and
wait until they have been cleared by hardware before trying to retrieve
the results of a read operation or setting a new write command.

[mchehab@s-opensource.com: make checkpatch happier]
Signed-off-by: Marcel Hasler <mahasler@gmail.com>
Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/usb/stk1160/stk1160-ac97.c

@@ -23,9 +23,30 @@
  *
  */
 
+#include <linux/delay.h>
+
 #include "stk1160.h"
 #include "stk1160-reg.h"
 
+static int stk1160_ac97_wait_transfer_complete(struct stk1160 *dev)
+{
+	unsigned long timeout = jiffies + msecs_to_jiffies(STK1160_AC97_TIMEOUT);
+	u8 value;
+
+	/* Wait for AC97 transfer to complete */
+	while (time_is_after_jiffies(timeout)) {
+		stk1160_read_reg(dev, STK1160_AC97CTL_0, &value);
+
+		if (!(value & (STK1160_AC97CTL_0_CR | STK1160_AC97CTL_0_CW)))
+			return 0;
+
+		usleep_range(50, 100);
+	}
+
+	stk1160_err("AC97 transfer took too long, this should never happen!");
+	return -EBUSY;
+}
+
 static void stk1160_write_ac97(struct stk1160 *dev, u16 reg, u16 value)
 {
 	/* Set codec register address */
@@ -35,11 +56,11 @@ static void stk1160_write_ac97(struct stk1160 *dev, u16 reg, u16 value)
 	stk1160_write_reg(dev, STK1160_AC97_CMD, value & 0xff);
 	stk1160_write_reg(dev, STK1160_AC97_CMD + 1, (value & 0xff00) >> 8);
 
-	/*
-	 * Set command write bit to initiate write operation.
-	 * The bit will be cleared when transfer is done.
-	 */
+	/* Set command write bit to initiate write operation */
 	stk1160_write_reg(dev, STK1160_AC97CTL_0, 0x8c);
+
+	/* Wait for command write bit to be cleared */
+	stk1160_ac97_wait_transfer_complete(dev);
 }
 
 #ifdef DEBUG
@@ -51,12 +72,14 @@ static u16 stk1160_read_ac97(struct stk1160 *dev, u16 reg)
 	/* Set codec register address */
 	stk1160_write_reg(dev, STK1160_AC97_ADDR, reg);
 
-	/*
-	 * Set command read bit to initiate read operation.
-	 * The bit will be cleared when transfer is done.
-	 */
+	/* Set command read bit to initiate read operation */
 	stk1160_write_reg(dev, STK1160_AC97CTL_0, 0x8b);
 
+	/* Wait for command read bit to be cleared */
+	if (stk1160_ac97_wait_transfer_complete(dev) < 0)
+		return 0;
+
+
 	/* Retrieve register value */
 	stk1160_read_reg(dev, STK1160_AC97_CMD, &vall);
 	stk1160_read_reg(dev, STK1160_AC97_CMD + 1, &valh);

drivers/media/usb/stk1160/stk1160-reg.h

@@ -122,6 +122,8 @@
 /* AC97 Audio Control */
 #define STK1160_AC97CTL_0		0x500
 #define STK1160_AC97CTL_1		0x504
+#define  STK1160_AC97CTL_0_CR		BIT(1)
+#define  STK1160_AC97CTL_0_CW		BIT(2)
 
 /* Use [0:6] bits of register 0x504 to set codec command address */
 #define STK1160_AC97_ADDR		0x504

drivers/media/usb/stk1160/stk1160.h

@@ -50,6 +50,8 @@
 #define STK1160_MAX_INPUT 4
 #define STK1160_SVIDEO_INPUT 4
 
+#define STK1160_AC97_TIMEOUT 50
+
 #define STK1160_I2C_TIMEOUT 100
 
 /* TODO: Print helpers