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>

1 files changed, 10 insertions, 0 deletions

diff --git a/drivers/block/mg_disk.c b/drivers/block/mg_disk.c
index 5b120eab2baa..6440d5945414 100644
--- a/drivers/block/mg_disk.c
+++ b/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 {