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authorOlof Johansson <olof@lixom.net>2006-04-12 22:52:33 -0400
committerPaul Mackerras <paulus@samba.org>2006-04-21 08:29:37 -0400
commit28897731318dc8f63f683eed9091e446916ad706 (patch)
tree702e9668705fcf96c0e1d6423a83f22d57e1c3fb /arch/powerpc
parent7daa411b810d7eadfaabe3765ec5f827893dbb30 (diff)
[PATCH] powerpc: Lower threshold for DART enablement to 1GB
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>
Diffstat (limited to 'arch/powerpc')
-rw-r--r--arch/powerpc/kernel/prom.c2
-rw-r--r--arch/powerpc/sysdev/dart_iommu.c12
2 files changed, 11 insertions, 3 deletions
diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 4336390bcf34..1cb69e8fb0b1 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -62,7 +62,7 @@ static int __initdata dt_root_addr_cells;
62static int __initdata dt_root_size_cells; 62static int __initdata dt_root_size_cells;
63 63
64#ifdef CONFIG_PPC64 64#ifdef CONFIG_PPC64
65static int __initdata iommu_is_off; 65int __initdata iommu_is_off;
66int __initdata iommu_force_on; 66int __initdata iommu_force_on;
67unsigned long tce_alloc_start, tce_alloc_end; 67unsigned long tce_alloc_start, tce_alloc_end;
68#endif 68#endif
diff --git a/arch/powerpc/sysdev/dart_iommu.c b/arch/powerpc/sysdev/dart_iommu.c
index 61d317428610..38087bd6e3cf 100644
--- a/arch/powerpc/sysdev/dart_iommu.c
+++ b/arch/powerpc/sysdev/dart_iommu.c
@@ -49,6 +49,7 @@
49 49
50#include "dart.h" 50#include "dart.h"
51 51
52extern int iommu_is_off;
52extern int iommu_force_on; 53extern int iommu_force_on;
53 54
54/* Physical base address and size of the DART table */ 55/* Physical base address and size of the DART table */
@@ -329,10 +330,17 @@ void iommu_init_early_dart(void)
329 330
330void __init alloc_dart_table(void) 331void __init alloc_dart_table(void)
331{ 332{
332 /* Only reserve DART space if machine has more than 2GB of RAM 333 /* Only reserve DART space if machine has more than 1GB of RAM
333 * or if requested with iommu=on on cmdline. 334 * or if requested with iommu=on on cmdline.
335 *
336 * 1GB of RAM is picked as limit because some default devices
337 * (i.e. Airport Extreme) have 30 bit address range limits.
334 */ 338 */
335 if (lmb_end_of_DRAM() <= 0x80000000ull && !iommu_force_on) 339
340 if (iommu_is_off)
341 return;
342
343 if (!iommu_force_on && lmb_end_of_DRAM() <= 0x40000000ull)
336 return; 344 return;
337 345
338 /* 512 pages (2MB) is max DART tablesize. */ 346 /* 512 pages (2MB) is max DART tablesize. */