diff options
| author | riastradh <riastradh@NetBSD.org> | 2019-12-02 08:33:42 +0000 |
|---|---|---|
| committer | riastradh <riastradh@NetBSD.org> | 2019-12-02 08:33:42 +0000 |
| commit | 4c6cbbdc0e6001a4ff1df346922e263ad8a30cf7 (patch) | |
| tree | 38da356879f4a25b7593275dd5fbdc28595bdf06 /sys/dev | |
| parent | ec9e7766cab543c54ab276510d61680bca1d8280 (diff) | |
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
Diffstat (limited to 'sys/dev')
| -rw-r--r-- | sys/dev/pci/pci_map.c | 24 |
1 files changed, 21 insertions, 3 deletions
diff --git a/sys/dev/pci/pci_map.c b/sys/dev/pci/pci_map.c index c54d0041bf0..2f724163add 100644 --- a/sys/dev/pci/pci_map.c +++ b/sys/dev/pci/pci_map.c @@ -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_attach_args *pa, int reg, pcireg_t type, 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) { |
