[src/jdolecek-ncq]: src/sys/dev/ata restore the fallback to non-NCQ on retrie...

[jdolecek <jdolecek%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/977723c76fff
branches:  jdolecek-ncq
changeset: 352752:977723c76fff
user:      jdolecek <jdolecek%NetBSD.org@localhost>
date:      Sun Aug 13 11:40:25 2017 +0000

description:
restore the fallback to non-NCQ on retries, do this after WDIORETRIES_SINGLE
retries, but only for non-FUA I/O; also only do the ATA_SINGLE fallback
when non-FUA

this makes sure that bio with ATA_SINGLE is not attempted as NCQ -
the ATA_SINGLE I/O is usually done using PIO by drivers which
actually support it, and thus are not compatible with DMA-only NCQ

diffstat:

 sys/dev/ata/wd.c |  24 +++++++++++++++++-------
 1 files changed, 17 insertions(+), 7 deletions(-)

diffs (54 lines):

diff -r 6116bf6437f5 -r 977723c76fff sys/dev/ata/wd.c
--- a/sys/dev/ata/wd.c  Sat Aug 12 22:43:22 2017 +0000
+++ b/sys/dev/ata/wd.c  Sun Aug 13 11:40:25 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: wd.c,v 1.428.2.32 2017/08/12 22:12:04 jdolecek Exp $ */
+/*     $NetBSD: wd.c,v 1.428.2.33 2017/08/13 11:40:25 jdolecek Exp $ */
 
 /*
  * Copyright (c) 1998, 2001 Manuel Bouyer.  All rights reserved.
@@ -54,7 +54,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: wd.c,v 1.428.2.32 2017/08/12 22:12:04 jdolecek Exp $");
+__KERNEL_RCSID(0, "$NetBSD: wd.c,v 1.428.2.33 2017/08/13 11:40:25 jdolecek Exp $");
 
 #include "opt_ata.h"
 #include "opt_wd.h"
@@ -720,9 +720,12 @@
        /*
         * If we're retrying, retry in single-sector mode. This will give us
         * the sector number of the problem, and will eventually allow the
-        * transfer to succeed.
+        * transfer to succeed. If FUA is requested, we can't actually
+        * do this, as ATA_SINGLE is usually executed as PIO transfer by drivers
+        * which support it, and that isn't compatible with NCQ/FUA.
         */
-       if (xfer->c_retries >= WDIORETRIES_SINGLE)
+       if (xfer->c_retries >= WDIORETRIES_SINGLE &&
+           (bp->b_flags & B_MEDIA_FUA) == 0)
                xfer->c_bio.flags = ATA_SINGLE;
        else
                xfer->c_bio.flags = 0;
@@ -734,10 +737,17 @@
                xfer->c_bio.flags |= ATA_LBA48;
 
        /*
-        * If NCQ was negotiated, always use it. Some drives return random
-        * errors when switching between NCQ and non-NCQ I/O too often. 
+        * If NCQ was negotiated, always use it for the first several attempts.
+        * Since device cancels all outstanding requests on error, downgrade
+        * to non-NCQ on retry, so that the retried transfer would not cause
+        * cascade failure for the other transfers if it fails again.
+        * If FUA was requested, we can't downgrade, as that would violate
+        * the semantics - FUA would not be honored. In that case, continue
+        * retrying with NCQ.
         */
-       if (wd->drvp->drive_flags & ATA_DRIVE_NCQ) {
+       if (wd->drvp->drive_flags & ATA_DRIVE_NCQ &&
+           (xfer->c_retries < WDIORETRIES_SINGLE ||
+           (bp->b_flags & B_MEDIA_FUA) != 0)) {
                xfer->c_bio.flags |= ATA_LBA48;
                xfer->c_flags |= C_NCQ;