[PATCHv2] ata: sata_dwc_460ex: preserve sactive_issued state across ISR invocations

[Rosen Penev <rosenp@gmail.com>]

Zeroing hsdev->sactive_issued on every ISR entry destroys the NCQ tag
tracking that must persist across interrupts.  This field is populated
in the NEWFP (DMA Setup FIS) handler and used in subsequent DMAT (DMA
Transfer Complete) interrupts to determine which tags have completed
via the formula tag_mask = (sactive_issued | sactive) ^ sactive.

With the zeroing in place, sactive_issued is always cleared before a
DMAT interrupt can read it, so the NCQ completion path never identifies
completed tags correctly.  The command completion then falls back to
the non-NCQ path using ap->link.active_tag, which works for a single
outstanding command but produces wrong results when multiple NCQ tags
are in flight.

Remove the spurious zeroing and fix the NCQ/non-NCQ discrimination:
when tag_mask is zero but the active command is NCQ, all tracked tags
are still in SCR_ACTIVE and no completion processing is needed.

Fixes: 2d20da00c324b ("ata: sata_dwc_460ex: get rid of global data")
Assisted-by: opencode:big-pickle
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 v2: resend as standalone patch
 drivers/ata/sata_dwc_460ex.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/ata/sata_dwc_460ex.c b/drivers/ata/sata_dwc_460ex.c
index 8a1d80ac906a..6cce790516cc 100644
--- a/drivers/ata/sata_dwc_460ex.c
+++ b/drivers/ata/sata_dwc_460ex.c
@@ -465,7 +465,6 @@ static irqreturn_t sata_dwc_isr(int irq, void *dev_instance)
 	int handled, port = 0;
 	uint intpr, sactive, sactive2, tag_mask;
 	struct sata_dwc_device_port *hsdevp;
-	hsdev->sactive_issued = 0;
 
 	spin_lock_irqsave(&host->lock, flags);
 
@@ -517,8 +516,11 @@ static irqreturn_t sata_dwc_isr(int irq, void *dev_instance)
 	sata_dwc_scr_read(&ap->link, SCR_ACTIVE, &sactive);
 	tag_mask = (hsdev->sactive_issued | sactive) ^ sactive;
 
-	/* If no sactive issued and tag_mask is zero then this is not NCQ */
-	if (hsdev->sactive_issued == 0 && tag_mask == 0) {
+	/*
+	 * If tag_mask is zero and the active command is not NCQ this is a
+	 * non-NCQ completion.
+	 */
+	if (tag_mask == 0) {
 		if (ap->link.active_tag == ATA_TAG_POISON)
 			tag = 0;
 		else
@@ -534,6 +536,12 @@ static irqreturn_t sata_dwc_isr(int irq, void *dev_instance)
 			handled = 1;
 			goto DONE;
 		}
+		if (ata_is_ncq(qc->tf.protocol)) {
+			/* NCQ commands still in flight; no tag completed. */
+			ap->ops->sff_check_status(ap);
+			handled = 1;
+			goto DONE;
+		}
 		status = ap->ops->sff_check_status(ap);
 
 		qc->ap->link.active_tag = tag;
@@ -612,9 +620,9 @@ static irqreturn_t sata_dwc_isr(int irq, void *dev_instance)
 		tag_mask &= ~(1U << tag);
 		qc = ata_qc_from_tag(ap, tag);
 		if (unlikely(!qc)) {
-			dev_err(ap->dev, "failed to get qc");
-			handled = 1;
-			goto DONE;
+			dev_err(ap->dev, "stale tag %d in NCQ completion",
+				tag);
+			continue;
 		}
 
 		/* To be picked up by completion functions */
@@ -1051,6 +1059,8 @@ static int sata_dwc_hardreset(struct ata_link *link, unsigned int *class,
 
 	ret = sata_sff_hardreset(link, class, deadline);
 
+	hsdev->sactive_issued = 0;
+
 	sata_dwc_enable_interrupts(hsdev);
 
 	/* Reconfigure the DMA control register */
-- 
2.55.0