[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>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index d25acd5..733a736 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -104,6 +104,9 @@
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
diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index 5c86ed6..0d65399 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -180,40 +180,81 @@
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