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[PATCH] powerpc: Lower threshold for DART enablement to 1GB

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Turn on the DART already at 1GB. This is needed because of crippled
devices in some systems, i.e. Airport Extreme cards, only supporting
30-bit DMA addresses.

Otherwise, users with between 1 and 2GB of memory will need to manually
enable it with iommu=force, and that's no good.

Some simple performance tests show that there's a slight impact of
enabling DART, but it's in the 1-3% range (kernel build with disk I/O
as well as over NFS).

iommu=off can still be used for those who don't want to deal with the
overhead (and don't need it for any devices).

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>
This commit is contained in:
Olof Johansson 2006-04-12 21:52:33 -05:00 committed by Paul Mackerras
parent 7daa411b81
commit 2889773131
2 changed files with 11 additions and 3 deletions
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2
arch/powerpc/kernel/prom.c
View File

@ -62,7 +62,7 @@ static int __initdata dt_root_addr_cells;
static int __initdata dt_root_size_cells;
#ifdef CONFIG_PPC64
static int __initdata iommu_is_off;
int __initdata iommu_is_off;
int __initdata iommu_force_on;
unsigned long tce_alloc_start, tce_alloc_end;
#endif

12
arch/powerpc/sysdev/dart_iommu.c
View File

@ -49,6 +49,7 @@
#include "dart.h"
extern int iommu_is_off;
extern int iommu_force_on;
/* Physical base address and size of the DART table */
@ -329,10 +330,17 @@ void iommu_init_early_dart(void)
void __init alloc_dart_table(void)
{
/* Only reserve DART space if machine has more than 2GB of RAM
/* Only reserve DART space if machine has more than 1GB of RAM
* or if requested with iommu=on on cmdline.
*
* 1GB of RAM is picked as limit because some default devices
* (i.e. Airport Extreme) have 30 bit address range limits.
*/
if (lmb_end_of_DRAM() <= 0x80000000ull && !iommu_force_on)
if (iommu_is_off)
return;
if (!iommu_force_on && lmb_end_of_DRAM() <= 0x40000000ull)
return;
/* 512 pages (2MB) is max DART tablesize. */