diff options
| author | Miod Vallat <miod@cvs.openbsd.org> | 2009-10-14 20:18:27 +0000 |
|---|---|---|
| committer | Miod Vallat <miod@cvs.openbsd.org> | 2009-10-14 20:18:27 +0000 |
| commit | 1a77f021b7c03d7faa5782b61acae3109fb4a6db (patch) | |
| tree | 77124decac83e3aeb4b40f2fc45c1d8820045ad3 /sys/arch | |
| parent | 51aed6c8450eb64de8050c8e63d6d39e005643ab (diff) | |
Add some comments to explain why the DMA32 physseg is really 2**31 bytes
long. Prompted by deraadt@ long ago.
Diffstat (limited to 'sys/arch')
| -rw-r--r-- | sys/arch/sgi/include/vmparam.h | 17 |
1 files changed, 14 insertions, 3 deletions
diff --git a/sys/arch/sgi/include/vmparam.h b/sys/arch/sgi/include/vmparam.h index 33f33aa2ff2..a55866983c4 100644 --- a/sys/arch/sgi/include/vmparam.h +++ b/sys/arch/sgi/include/vmparam.h @@ -1,12 +1,23 @@ -/* $OpenBSD: vmparam.h,v 1.3 2009/05/08 18:42:04 miod Exp $ */ - +/* $OpenBSD: vmparam.h,v 1.4 2009/10/14 20:18:26 miod Exp $ */ +/* public domain */ #ifndef _SGI_VMPARAM_H_ #define _SGI_VMPARAM_H_ #define VM_PHYSSEG_MAX 32 /* Max number of physical memory segments */ +/* + * On Origin and Octane families, DMA to 32-bit PCI devices is restricted. + * + * Systems with physical memory after the 2GB boundary needs to ensure + * memory which may used for DMA transfers is allocated from the low + * memory range. + * + * Other systems, like the O2, do not have such a restriction, but can not + * have more than 2GB of physical memory, so this doesn't affect them. + */ + #define VM_NFREELIST 2 -#define VM_FREELIST_DMA32 1 /* memory under 2GB suitable for DMA */ +#define VM_FREELIST_DMA32 1 /* memory suitable for 32-bit DMA */ #include <mips64/vmparam.h> |