sata_mv wait for empty+idle

When performing EH, it is recommended to wait for the EDMA engine
to empty out requests-in-progress before disabling EDMA.

Introduce code to poll the EDMA_STATUS register for idle/empty bits
before disabling EDMA.  For non-EH operation, this will normally exit
without delay, other than the register read.

A later series of patches may focus on eliminating this and various
other register reads (when possible) throughout the driver,
but for now we're focussing on solid reliablity.

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/drivers/ata/sata_mv.c b/drivers/ata/sata_mv.c
index 10ef9683f048..692996216b1a 100644
--- a/drivers/ata/sata_mv.c
+++ b/drivers/ata/sata_mv.c
@@ -888,6 +888,25 @@ static void mv_start_dma(struct ata_port *ap, void __iomem *port_mmio,
         }
 }
 
+static void mv_wait_for_edma_empty_idle(struct ata_port *ap)
+{
+        void __iomem *port_mmio = mv_ap_base(ap);
+        const u32 empty_idle = (EDMA_STATUS_CACHE_EMPTY | EDMA_STATUS_IDLE);
+        const int per_loop = 5, timeout = (15 * 1000 / per_loop);
+        int i;
+
+        /*
+         * Wait for the EDMA engine to finish transactions in progress.
+         */
+        for (i = 0; i < timeout; ++i) {
+                u32 edma_stat = readl(port_mmio + EDMA_STATUS_OFS);
+                if ((edma_stat & empty_idle) == empty_idle)
+                        break;
+                udelay(per_loop);
+        }
+        /* ata_port_printk(ap, KERN_INFO, "%s: %u+ usecs\n", __func__, i); */
+}
+
 /**
  *      mv_stop_edma_engine - Disable eDMA engine
  *      @port_mmio: io base address
@@ -920,6 +939,7 @@ static int mv_stop_edma(struct ata_port *ap)
         if (!(pp->pp_flags & MV_PP_FLAG_EDMA_EN))
                 return 0;
         pp->pp_flags &= ~MV_PP_FLAG_EDMA_EN;
+        mv_wait_for_edma_empty_idle(ap);
         if (mv_stop_edma_engine(port_mmio)) {
                 ata_port_printk(ap, KERN_ERR, "Unable to stop eDMA\n");
                 return -EIO;