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>

1 files changed, 13 insertions, 2 deletions

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 986e3324e302..7c4f886f1f16 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -556,16 +556,27 @@ static inline void __iomem *ahci_port_base(struct ata_port *ap)
 
 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);
 }
 
 /**