[patch 16/29] ahci: retry enabling AHCI a few times before spitting out WARN_ON()

[Greg KH <gregkh@suse.de>]

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2.6.25-stable review patch.  If anyone has any objections, please let us 
know.

------------------
From: Tejun Heo <htejun@gmail.com>

commit 15fe982e429e0e6b7466719acb6cfd9dbfe47f0c upstream

ahci: retry enabling AHCI a few times before spitting out WARN_ON()

Some chips need AHCI_EN set more than once to actually set it.  Try a
few times before giving up and spitting out WARN_ON().

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Peer Chen <pchen@nvidia.com>
Cc: Volker Armin Hemmann <volker.armin.hemmann@tu-clausthal.de>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 drivers/ata/ahci.c |   15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -634,16 +634,27 @@ static inline void __iomem *ahci_port_ba
 
 static void ahci_enable_ahci(void __iomem *mmio)
 {
+	int i;
 	u32 tmp;
 
 	/* turn on AHCI_EN */
 	tmp = readl(mmio + HOST_CTL);
-	if (!(tmp & HOST_AHCI_EN)) {
+	if (tmp & HOST_AHCI_EN)
+		return;
+
+	/* Some controllers need AHCI_EN to be written multiple times.
+	 * Try a few times before giving up.
+	 */
+	for (i = 0; i < 5; i++) {
 		tmp |= HOST_AHCI_EN;
 		writel(tmp, mmio + HOST_CTL);
 		tmp = readl(mmio + HOST_CTL);	/* flush && sanity check */
-		WARN_ON(!(tmp & HOST_AHCI_EN));
+		if (tmp & HOST_AHCI_EN)
+			return;
+		msleep(10);
 	}
+
+	WARN_ON(1);
 }
 
 /**

--