[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>

diff --git a/drivers/ata/ahci.c b/drivers/ata/ahci.c
index 9f3c591..b615390 100644 (file)
--- 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 */