libata: ahci_start_engine compliant to AHCI spec

At the end of section 10.1 of AHCI spec (rev 1.3), it states

Software shall not set PxCMD.ST to 1 until it is determined that
a functoinal device is present on the port as determined by
PxTFD.STS.BSY=0, PxTFD.STS.DRQ=0 and PxSSTS.DET=3h

Even though most AHCI host controller works without this check,
specific controller will fail under this condition.

Signed-off-by: Jian Peng <jipeng2005@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index d38c40fe4ddb..ff9d832a163d 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -561,6 +561,27 @@ void ahci_start_engine(struct ata_port *ap)
 {
         void __iomem *port_mmio = ahci_port_base(ap);
         u32 tmp;
+        u8 status;
+
+        status = readl(port_mmio + PORT_TFDATA) & 0xFF;
+
+        /*
+         * At end of section 10.1 of AHCI spec (rev 1.3), it states
+         * Software shall not set PxCMD.ST to 1 until it is determined
+         * that a functoinal device is present on the port as determined by
+         * PxTFD.STS.BSY=0, PxTFD.STS.DRQ=0 and PxSSTS.DET=3h
+         *
+         * Even though most AHCI host controllers work without this check,
+         * specific controller will fail under this condition
+         */
+        if (status & (ATA_BUSY | ATA_DRQ))
+                return;
+        else {
+                ahci_scr_read(&ap->link, SCR_STATUS, &tmp);
+
+                if ((tmp & 0xf) != 0x3)
+                        return;
+        }
 
         /* start DMA */
         tmp = readl(port_mmio + PORT_CMD);