linux-kernel - [PATCH 2/2] mg_disk: fix reading invalid status when use polling driver

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Date:	Thu, 23 Jul 2009 13:57:46 +0900
From:	unsik Kim <donari75@...il.com>
To:	axboe@...nel.dk, tj@...nel.org
Cc:	linux-kernel@...r.kernel.org, unsik Kim <donari75@...il.com>
Subject: [PATCH 2/2] 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@...il.com>
---
 drivers/block/mg_disk.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/drivers/block/mg_disk.c b/drivers/block/mg_disk.c
index 26371d5..6d7fbaa 100644
--- a/drivers/block/mg_disk.c
+++ b/drivers/block/mg_disk.c
@@ -218,6 +218,16 @@ 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 {
-- 
1.6.0.6

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