mg_disk: fix reading invalid status when use polling driver

When using polling driver, little delay is required to access
status register. Without this, host might read invalid status.
Signed-off-by: unsik Kim <donari75@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/block/mg_disk.c

@@ -219,6 +219,16 @@ static unsigned int mg_wait(struct mg_host *host, u32 expect, u32 msec)
 	host->error = MG_ERR_NONE;
 	expire = jiffies + msecs_to_jiffies(msec);
 
+	/* These 2 times dummy status read prevents reading invalid
+	 * status. A very little time (3 times of mflash operating clk)
+	 * is required for busy bit is set. Use dummy read instead of
+	 * busy wait, because mflash's PLL is machine dependent.
+	 */
+	if (prv_data->use_polling) {
+		status = inb((unsigned long)host->dev_base + MG_REG_STATUS);
+		status = inb((unsigned long)host->dev_base + MG_REG_STATUS);
+	}
+
 	status = inb((unsigned long)host->dev_base + MG_REG_STATUS);
 
 	do {