aacraid: reduce max I/O size to avoid DMA issues

Reserve one page for the DMA subsystem, that may need it when the I/O
buffer is not page aligned.

Without this change, writes with the maximum allowed size failed, if:
- physical memory was fragmented, making it necessary to use one DMA
  segment for each page
- the buffer to be written was not page aligned, causing the DMA
  subsystem to need one extra segment

In the scenario above, the DMA subsystem would run out of segments,
resulting in a write with no SG segments, that would fail.

Reviewed by:		imp
MFC after:		2 weeks
Sponsored by:		Instituto de Pesquisas Eldorado (eldorado.org.br)
Differential Revision:	https://reviews.freebsd.org/D30798

3 files changed, 11 insertions, 3 deletions

diff --git a/sys/dev/aacraid/aacraid.c b/sys/dev/aacraid/aacraid.c
index 65c585269b78..51a633e70515 100644
--- a/sys/dev/aacraid/aacraid.c
+++ b/sys/dev/aacraid/aacraid.c
@@ -579,7 +579,7 @@ aac_alloc(struct aac_softc *sc)
 			       BUS_SPACE_MAXADDR_32BIT,	/* lowaddr */
 			       BUS_SPACE_MAXADDR, 	/* highaddr */
 			       NULL, NULL, 		/* filter, filterarg */
-			       sc->aac_max_sectors << 9, /* maxsize */
+			       AAC_MAXIO_SIZE(sc),	/* maxsize */
 			       sc->aac_sg_tablesize,	/* nsegments */
 			       BUS_SPACE_MAXSIZE_32BIT,	/* maxsegsize */
 			       BUS_DMA_ALLOCNOW,	/* flags */
@@ -1807,7 +1807,7 @@ aac_init(struct aac_softc *sc)
 	}
 
 	ip->MaxIoCommands = sc->aac_max_fibs;
-	ip->MaxIoSize = sc->aac_max_sectors << 9;
+	ip->MaxIoSize = AAC_MAXIO_SIZE(sc);
 	ip->MaxFibSize = sc->aac_max_fib_size;
 
 	aac_adapter_init_tole(ip);
diff --git a/sys/dev/aacraid/aacraid_cam.c b/sys/dev/aacraid/aacraid_cam.c
index 48da7e8d757f..9c73248472bd 100644
--- a/sys/dev/aacraid/aacraid_cam.c
+++ b/sys/dev/aacraid/aacraid_cam.c
@@ -1011,7 +1011,7 @@ aac_cam_action(struct cam_sim *sim, union ccb *ccb)
 		cpi->max_lun = 7;	/* Per the controller spec */
 		cpi->initiator_id = camsc->inf->InitiatorBusId;
 		cpi->bus_id = camsc->inf->BusNumber;
-		cpi->maxio = sc->aac_max_sectors << 9;
+		cpi->maxio = AAC_MAXIO_SIZE(sc);
 
 		/*
 		 * Resetting via the passthrough or parallel bus scan
diff --git a/sys/dev/aacraid/aacraid_var.h b/sys/dev/aacraid/aacraid_var.h
index 4fed21b1356b..bbafdafb8840 100644
--- a/sys/dev/aacraid/aacraid_var.h
+++ b/sys/dev/aacraid/aacraid_var.h
@@ -471,6 +471,14 @@ struct aac_softc
 };
 
 /*
+ * Max. I/O size in bytes.
+ * Reserve one page for the DMA subsystem, that may need it when the
+ * I/O buffer is not page aligned.
+ */
+#define AAC_MAXIO_SIZE(sc)	MIN(((sc)->aac_max_sectors << 9) - PAGE_SIZE, \
+					maxphys)
+
+/*
  * Event callback mechanism for the driver
  */
 #define AAC_EVENT_NONE		0x00