sata_nv: don't use legacy DMA in ADMA mode (v3)

We need to run any DMA command with result taskfile requested in ADMA mode
when the port is in ADMA mode, otherwise it may try to use the legacy DMA engine
in ADMA mode which is not allowed. Enforce this with BUG_ON() since data
corruption could potentially result if this happened. Also, fail any attempt to
try and issue NCQ commands with result taskfile requested, since the hardware
doesn't allow this.

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

drivers/ata/sata_nv.c

@@ -791,11 +791,13 @@ static int nv_adma_check_atapi_dma(struct ata_queued_cmd *qc)
 
 static void nv_adma_tf_read(struct ata_port *ap, struct ata_taskfile *tf)
 {
-	/* Since commands where a result TF is requested are not
-	   executed in ADMA mode, the only time this function will be called
-	   in ADMA mode will be if a command fails. In this case we
-	   don't care about going into register mode with ADMA commands
-	   pending, as the commands will all shortly be aborted anyway. */
+	/* Other than when internal or pass-through commands are executed,
+	   the only time this function will be called in ADMA mode will be
+	   if a command fails. In the failure case we don't care about going
+	   into register mode with ADMA commands pending, as the commands will
+	   all shortly be aborted anyway. We assume that NCQ commands are not
+	   issued via passthrough, which is the only way that switching into
+	   ADMA mode could abort outstanding commands. */
 	nv_adma_register_mode(ap);
 
 	ata_tf_read(ap, tf);
@@ -1359,11 +1361,9 @@ static int nv_adma_use_reg_mode(struct ata_queued_cmd *qc)
 	struct nv_adma_port_priv *pp = qc->ap->private_data;
 
 	/* ADMA engine can only be used for non-ATAPI DMA commands,
-	   or interrupt-driven no-data commands, where a result taskfile
-	   is not required. */
+	   or interrupt-driven no-data commands. */
 	if ((pp->flags & NV_ADMA_ATAPI_SETUP_COMPLETE) ||
-	   (qc->tf.flags & ATA_TFLAG_POLLING) ||
-	   (qc->flags & ATA_QCFLAG_RESULT_TF))
+	   (qc->tf.flags & ATA_TFLAG_POLLING))
 		return 1;
 
 	if ((qc->flags & ATA_QCFLAG_DMAMAP) ||
@@ -1381,6 +1381,8 @@ static void nv_adma_qc_prep(struct ata_queued_cmd *qc)
 		       NV_CPB_CTL_IEN;
 
 	if (nv_adma_use_reg_mode(qc)) {
+		BUG_ON(!(pp->flags & NV_ADMA_ATAPI_SETUP_COMPLETE) &&
+			(qc->flags & ATA_QCFLAG_DMAMAP));
 		nv_adma_register_mode(qc->ap);
 		ata_qc_prep(qc);
 		return;
@@ -1425,9 +1427,21 @@ static unsigned int nv_adma_qc_issue(struct ata_queued_cmd *qc)
 
 	VPRINTK("ENTER\n");
 
+	/* We can't handle result taskfile with NCQ commands, since
+	   retrieving the taskfile switches us out of ADMA mode and would abort
+	   existing commands. */
+	if (unlikely(qc->tf.protocol == ATA_PROT_NCQ &&
+		     (qc->flags & ATA_QCFLAG_RESULT_TF))) {
+		ata_dev_printk(qc->dev, KERN_ERR,
+			"NCQ w/ RESULT_TF not allowed\n");
+		return AC_ERR_SYSTEM;
+	}
+
 	if (nv_adma_use_reg_mode(qc)) {
 		/* use ATA register mode */
 		VPRINTK("using ATA register mode: 0x%lx\n", qc->flags);
+		BUG_ON(!(pp->flags & NV_ADMA_ATAPI_SETUP_COMPLETE) &&
+			(qc->flags & ATA_QCFLAG_DMAMAP));
 		nv_adma_register_mode(qc->ap);
 		return ata_qc_issue_prot(qc);
 	} else