V4L/DVB: cx25840: Make cx25840 i2c register read transactions atomic

There was a small window between writing the cx25840 register
address over the i2c bus and reading the register contents back from the
cx25840 device that the i2c adapter lock was released.  This change ensures the
adapter lock is not released until the register read is done.
Signed-off-by: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/cx25840/cx25840-core.c

@@ -80,33 +80,53 @@ int cx25840_write4(struct i2c_client *client, u16 addr, u32 value)
 
 u8 cx25840_read(struct i2c_client * client, u16 addr)
 {
-	u8 buffer[2];
-	buffer[0] = addr >> 8;
-	buffer[1] = addr & 0xff;
-
-	if (i2c_master_send(client, buffer, 2) < 2)
-		return 0;
-
-	if (i2c_master_recv(client, buffer, 1) < 1)
+	struct i2c_msg msgs[2];
+	u8 tx_buf[2], rx_buf[1];
+
+	/* Write register address */
+	tx_buf[0] = addr >> 8;
+	tx_buf[1] = addr & 0xff;
+	msgs[0].addr = client->addr;
+	msgs[0].flags = 0;
+	msgs[0].len = 2;
+	msgs[0].buf = (char *) tx_buf;
+
+	/* Read data from register */
+	msgs[1].addr = client->addr;
+	msgs[1].flags = I2C_M_RD;
+	msgs[1].len = 1;
+	msgs[1].buf = (char *) rx_buf;
+
+	if (i2c_transfer(client->adapter, msgs, 2) < 2)
 		return 0;
 
-	return buffer[0];
+	return rx_buf[0];
 }
 
 u32 cx25840_read4(struct i2c_client * client, u16 addr)
 {
-	u8 buffer[4];
-	buffer[0] = addr >> 8;
-	buffer[1] = addr & 0xff;
-
-	if (i2c_master_send(client, buffer, 2) < 2)
-		return 0;
-
-	if (i2c_master_recv(client, buffer, 4) < 4)
+	struct i2c_msg msgs[2];
+	u8 tx_buf[2], rx_buf[4];
+
+	/* Write register address */
+	tx_buf[0] = addr >> 8;
+	tx_buf[1] = addr & 0xff;
+	msgs[0].addr = client->addr;
+	msgs[0].flags = 0;
+	msgs[0].len = 2;
+	msgs[0].buf = (char *) tx_buf;
+
+	/* Read data from registers */
+	msgs[1].addr = client->addr;
+	msgs[1].flags = I2C_M_RD;
+	msgs[1].len = 4;
+	msgs[1].buf = (char *) rx_buf;
+
+	if (i2c_transfer(client->adapter, msgs, 2) < 2)
 		return 0;
 
-	return (buffer[3] << 24) | (buffer[2] << 16) |
-	    (buffer[1] << 8) | buffer[0];
+	return (rx_buf[3] << 24) | (rx_buf[2] << 16) | (rx_buf[1] << 8) |
+		rx_buf[0];
 }
 
 int cx25840_and_or(struct i2c_client *client, u16 addr, unsigned and_mask,