[libata] AHCI: enable AHCI mode, before using AHCI reset

AHCI spec says host-reset bit may only be set when the ahci-enable bit
is also set.

Noticed by Peer Chen <peerchen@gmail.com>

Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 9f3c591c721..b615390b6b8 100644
--- a/drivers/ata/ahci.c
+++ b/drivers/ata/ahci.c
@@ -827,8 +827,14 @@ static int ahci_reset_controller(struct ata_host *host)
         void __iomem *mmio = host->iomap[AHCI_PCI_BAR];
         u32 tmp;
 
-        /* global controller reset */
+        /* we must be in AHCI mode, before using anything
+         * AHCI-specific, such as HOST_RESET.
+         */
         tmp = readl(mmio + HOST_CTL);
+        if (!(tmp & HOST_AHCI_EN))
+                writel(tmp | HOST_AHCI_EN, mmio + HOST_CTL);
+
+        /* global controller reset */
         if ((tmp & HOST_RESET) == 0) {
                 writel(tmp | HOST_RESET, mmio + HOST_CTL);
                 readl(mmio + HOST_CTL); /* flush */