[PATCH] x86-64: improved iommu documentation

- add SWIOTLB config help text
- mention Documentation/x86_64/boot-options.txt in
  Documentation/kernel-parameters.txt
- remove the duplication of the iommu kernel parameter documentation.
- Better explanation of some of the iommu kernel parameter options.
- "32MB<<order" instead of "32MB^order".
- Mention the default "order" value.
- list the four existing PCI-DMA mapping implementations of arch x86_64
- group the iommu= option keywords by PCI-DMA mapping implementation.
- Distinguish iommu= option keywords from number arguments.
- Explain the meaning of DAC and SAC.

Signed-off-by: Karsten Weiss <knweiss@science-computing.de>
Signed-off-by: Andi Kleen <ak@suse.de>
Acked-by: Muli Ben-Yehuda <muli@il.ibm.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
This commit is contained in:
Karsten Weiss 2007-02-13 13:26:21 +01:00 committed by Andi Kleen
parent 5809f9d442
commit 5558870bfb
4 changed files with 86 additions and 56 deletions

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@ -104,6 +104,9 @@ loader, and have no meaning to the kernel directly.
Do not modify the syntax of boot loader parameters without extreme
need or coordination with <Documentation/i386/boot.txt>.
There are also arch-specific kernel-parameters not documented here.
See for example <Documentation/x86_64/boot-options.txt>.
Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
a trailing = on the name of any parameter states that that parameter will
be entered as an environment variable, whereas its absence indicates that

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@ -180,40 +180,81 @@ PCI
pci=lastbus=NUMBER Scan upto NUMBER busses, no matter what the mptable says.
pci=noacpi Don't use ACPI to set up PCI interrupt routing.
IOMMU
IOMMU (input/output memory management unit)
iommu=[size][,noagp][,off][,force][,noforce][,leak][,memaper[=order]][,merge]
[,forcesac][,fullflush][,nomerge][,noaperture][,calgary]
size set size of iommu (in bytes)
noagp don't initialize the AGP driver and use full aperture.
off don't use the IOMMU
leak turn on simple iommu leak tracing (only when CONFIG_IOMMU_LEAK is on)
memaper[=order] allocate an own aperture over RAM with size 32MB^order.
noforce don't force IOMMU usage. Default.
force Force IOMMU.
merge Do SG merging. Implies force (experimental)
nomerge Don't do SG merging.
forcesac For SAC mode for masks <40bits (experimental)
fullflush Flush IOMMU on each allocation (default)
nofullflush Don't use IOMMU fullflush
allowed overwrite iommu off workarounds for specific chipsets.
soft Use software bounce buffering (default for Intel machines)
noaperture Don't touch the aperture for AGP.
allowdac Allow DMA >4GB
When off all DMA over >4GB is forced through an IOMMU or bounce
buffering.
nodac Forbid DMA >4GB
panic Always panic when IOMMU overflows
calgary Use the Calgary IOMMU if it is available
Currently four x86-64 PCI-DMA mapping implementations exist:
swiotlb=pages[,force]
1. <arch/x86_64/kernel/pci-nommu.c>: use no hardware/software IOMMU at all
(e.g. because you have < 3 GB memory).
Kernel boot message: "PCI-DMA: Disabling IOMMU"
pages Prereserve that many 128K pages for the software IO bounce buffering.
force Force all IO through the software TLB.
2. <arch/x86_64/kernel/pci-gart.c>: AMD GART based hardware IOMMU.
Kernel boot message: "PCI-DMA: using GART IOMMU"
calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
calgary=[translate_empty_slots]
calgary=[disable=<PCI bus number>]
3. <arch/x86_64/kernel/pci-swiotlb.c> : Software IOMMU implementation. Used
e.g. if there is no hardware IOMMU in the system and it is need because
you have >3GB memory or told the kernel to us it (iommu=soft))
Kernel boot message: "PCI-DMA: Using software bounce buffering
for IO (SWIOTLB)"
4. <arch/x86_64/pci-calgary.c> : IBM Calgary hardware IOMMU. Used in IBM
pSeries and xSeries servers. This hardware IOMMU supports DMA address
mapping with memory protection, etc.
Kernel boot message: "PCI-DMA: Using Calgary IOMMU"
iommu=[<size>][,noagp][,off][,force][,noforce][,leak[=<nr_of_leak_pages>]
[,memaper[=<order>]][,merge][,forcesac][,fullflush][,nomerge]
[,noaperture][,calgary]
General iommu options:
off Don't initialize and use any kind of IOMMU.
noforce Don't force hardware IOMMU usage when it is not needed.
(default).
force Force the use of the hardware IOMMU even when it is
not actually needed (e.g. because < 3 GB memory).
soft Use software bounce buffering (SWIOTLB) (default for
Intel machines). This can be used to prevent the usage
of an available hardware IOMMU.
iommu options only relevant to the AMD GART hardware IOMMU:
<size> Set the size of the remapping area in bytes.
allowed Overwrite iommu off workarounds for specific chipsets.
fullflush Flush IOMMU on each allocation (default).
nofullflush Don't use IOMMU fullflush.
leak Turn on simple iommu leak tracing (only when
CONFIG_IOMMU_LEAK is on). Default number of leak pages
is 20.
memaper[=<order>] Allocate an own aperture over RAM with size 32MB<<order.
(default: order=1, i.e. 64MB)
merge Do scather-gather (SG) merging. Implies "force"
(experimental).
nomerge Don't do scather-gather (SG) merging.
noaperture Ask the IOMMU not to touch the aperture for AGP.
forcesac Force single-address cycle (SAC) mode for masks <40bits
(experimental).
noagp Don't initialize the AGP driver and use full aperture.
allowdac Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
DAC is used with 32-bit PCI to push a 64-bit address in
two cycles. When off all DMA over >4GB is forced through
an IOMMU or software bounce buffering.
nodac Forbid DAC mode, i.e. DMA >4GB.
panic Always panic when IOMMU overflows.
calgary Use the Calgary IOMMU if it is available
iommu options only relevant to the software bounce buffering (SWIOTLB) IOMMU
implementation:
swiotlb=<pages>[,force]
<pages> Prereserve that many 128K pages for the software IO
bounce buffering.
force Force all IO through the software TLB.
Settings for the IBM Calgary hardware IOMMU currently found in IBM
pSeries and xSeries machines:
calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
calgary=[translate_empty_slots]
calgary=[disable=<PCI bus number>]
panic Always panic when IOMMU overflows
64k,...,8M - Set the size of each PCI slot's translation table
when using the Calgary IOMMU. This is the size of the translation

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@ -458,8 +458,8 @@ config IOMMU
on systems with more than 3GB. This is usually needed for USB,
sound, many IDE/SATA chipsets and some other devices.
Provides a driver for the AMD Athlon64/Opteron/Turion/Sempron GART
based IOMMU and a software bounce buffer based IOMMU used on Intel
systems and as fallback.
based hardware IOMMU and a software bounce buffer based IOMMU used
on Intel systems and as fallback.
The code is only active when needed (enough memory and limited
device) unless CONFIG_IOMMU_DEBUG or iommu=force is specified
too.
@ -496,6 +496,12 @@ config CALGARY_IOMMU_ENABLED_BY_DEFAULT
# need this always selected by IOMMU for the VIA workaround
config SWIOTLB
bool
help
Support for software bounce buffers used on x86-64 systems
which don't have a hardware IOMMU (e.g. the current generation
of Intel's x86-64 CPUs). Using this PCI devices which can only
access 32-bits of memory can be used on systems with more than
3 GB of memory. If unsure, say Y.
config X86_MCE
bool "Machine check support" if EMBEDDED

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@ -223,30 +223,10 @@ int dma_set_mask(struct device *dev, u64 mask)
}
EXPORT_SYMBOL(dma_set_mask);
/* iommu=[size][,noagp][,off][,force][,noforce][,leak][,memaper[=order]][,merge]
[,forcesac][,fullflush][,nomerge][,biomerge]
size set size of iommu (in bytes)
noagp don't initialize the AGP driver and use full aperture.
off don't use the IOMMU
leak turn on simple iommu leak tracing (only when CONFIG_IOMMU_LEAK is on)
memaper[=order] allocate an own aperture over RAM with size 32MB^order.
noforce don't force IOMMU usage. Default.
force Force IOMMU.
merge Do lazy merging. This may improve performance on some block devices.
Implies force (experimental)
biomerge Do merging at the BIO layer. This is more efficient than merge,
but should be only done with very big IOMMUs. Implies merge,force.
nomerge Don't do SG merging.
forcesac For SAC mode for masks <40bits (experimental)
fullflush Flush IOMMU on each allocation (default)
nofullflush Don't use IOMMU fullflush
allowed overwrite iommu off workarounds for specific chipsets.
soft Use software bounce buffering (default for Intel machines)
noaperture Don't touch the aperture for AGP.
allowdac Allow DMA >4GB
nodac Forbid DMA >4GB
panic Force panic when IOMMU overflows
*/
/*
* See <Documentation/x86_64/boot-options.txt> for the iommu kernel parameter
* documentation.
*/
__init int iommu_setup(char *p)
{
iommu_merge = 1;