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>

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);