Module Name: src
Committed By: riastradh
Date: Mon Dec 2 08:33:42 UTC 2019
Modified Files:
src/sys/dev/pci: pci_map.c
Log Message:
Use BUS_SPACE_MAP_PREFETCHABLE only if BAR and driver agree on it.
- A driver that expects prefetchable memory and knows to issue the
needed bus_space_barrier calls can pass BUS_SPACE_MAP_PREFETCHABLE
to indicate a desire to map the memory prefetchable if the BAR
allows it.
(A driver that _really wants_ BUS_SPACE_MAP_PREFETCHABLE even if
the BAR claims _not_ to be prefetchable can use pci_mapreg_info and
bus_space_map explicitly -- this is not different from what we have
today.)
- For a driver that _does not_ expect prefetchable memory, the
appearance of the prefetchable bit in the BAR shouldn't cause it to
use BUS_SPACE_MAP_PREFETCHABLE, because the driver will not issue
the needed bus_space_barrier calls to get sensible results.
Note: `Prefetchable' here, sometimes called `write-combining', means
reads have no side effects, and writes are idempotent, so it is safe
to issue reads out of order and safe to combine writes.
Mappings with BUS_SPACE_MAP_PREFETCHABLE are often more weakly
ordered than normal memory -- e.g., on x86, in WC-type memory
regions, loads can be reordered with loads, stores can be reordered
with stores, which is not possible with any other type of memory
regions.
Discussed on tech-kern a while ago:
https://mail-index.NetBSD.org/tech-kern/2017/03/22/msg021678.html
This is option A, which received the most support. This should help
unconfuse drivers that do not expect prefetchable mappings, like
Yamaguchi-san tripped over recently:
https://mail-index.NetBSD.org/tech-kern/2019/12/02/msg025785.html
To generate a diff of this commit:
cvs rdiff -u -r1.37 -r1.38 src/sys/dev/pci/pci_map.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/dev/pci/pci_map.c
diff -u src/sys/dev/pci/pci_map.c:1.37 src/sys/dev/pci/pci_map.c:1.38
--- src/sys/dev/pci/pci_map.c:1.37 Fri Mar 1 05:41:56 2019
+++ src/sys/dev/pci/pci_map.c Mon Dec 2 08:33:42 2019
@@ -1,4 +1,4 @@
-/* $NetBSD: pci_map.c,v 1.37 2019/03/01 05:41:56 msaitoh Exp $ */
+/* $NetBSD: pci_map.c,v 1.38 2019/12/02 08:33:42 riastradh Exp $ */
/*-
* Copyright (c) 1998, 2000 The NetBSD Foundation, Inc.
@@ -34,7 +34,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: pci_map.c,v 1.37 2019/03/01 05:41:56 msaitoh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: pci_map.c,v 1.38 2019/12/02 08:33:42 riastradh Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@@ -328,7 +328,25 @@ pci_mapreg_submap(const struct pci_attac
if (realmaxsize < (offset + reqsize))
return 1;
- if (bus_space_map(tag, base, reqsize, busflags | flags, &handle))
+ /*
+ * If the BAR doesn't say prefetchable, assume the mapping
+ * cannot be prefetchable. In other words, we will use
+ * BUS_SPACE_MAP_PREFETCHABLE only if the driver requested it
+ * _and_ the BAR indicates it is prefetchable.
+ *
+ * Drivers that expect prefetchable memory will issue the
+ * appropriate barriers, whereas drivers that do not expect
+ * prefetchable memory will be terribly confused if the memory
+ * is mapped prefetchable.
+ *
+ * Drivers that want to override the BAR and map it with
+ * BUS_SPACE_MAP_PREFETCHABLE anyway can use pci_mapreg_map and
+ * bus_space_map explicitly.
+ */
+ if (!ISSET(flags, BUS_SPACE_MAP_PREFETCHABLE))
+ busflags &= ~BUS_SPACE_MAP_PREFETCHABLE;
+
+ if (bus_space_map(tag, base, reqsize, busflags, &handle))
return 1;
if (pci_mapreg_map_enable_decode) {
