sata_nv: delay on switching between NCQ and non-NCQ commands

This patch appears to solve some problems with commands timing out in
cases where an NCQ command is immediately followed by a non-NCQ command
(or possibly vice versa). This is a rather ugly solution, but until we
know more about why this is needed, this is about all we can do.

Signed-off-by: Robert Hancock <hancockr@shaw.ca>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

diff --git a/drivers/ata/sata_nv.c b/drivers/ata/sata_nv.c
index f1fea96..b93e64d 100644 (file)
--- a/drivers/ata/sata_nv.c
+++ b/drivers/ata/sata_nv.c
@@ -219,6 +219,7 @@ struct nv_adma_port_priv {
        void __iomem *          gen_block;
        void __iomem *          notifier_clear_block;
        u8                      flags;
+       int                     last_issue_ncq;
 };
 
 struct nv_host_priv {
@@ -1260,6 +1261,7 @@ static unsigned int nv_adma_qc_issue(struct ata_queued_cmd *qc)
 {
        struct nv_adma_port_priv *pp = qc->ap->private_data;
        void __iomem *mmio = pp->ctl_block;
+       int curr_ncq = (qc->tf.protocol == ATA_PROT_NCQ);
 
        VPRINTK("ENTER\n");
 
@@ -1274,6 +1276,14 @@ static unsigned int nv_adma_qc_issue(struct ata_queued_cmd *qc)
        /* write append register, command tag in lower 8 bits
           and (number of cpbs to append -1) in top 8 bits */
        wmb();
+
+       if(curr_ncq != pp->last_issue_ncq) {
+               /* Seems to need some delay before switching between NCQ and non-NCQ
+                  commands, else we get command timeouts and such. */
+               udelay(20);
+               pp->last_issue_ncq = curr_ncq;
+       }
+
        writew(qc->tag, mmio + NV_ADMA_APPEND);
 
        DPRINTK("Issued tag %u\n",qc->tag);