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Commit 5558870b authored by Karsten Weiss's avatar Karsten Weiss Committed by Andi Kleen
Browse files

[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: default avatarKarsten Weiss <knweiss@science-computing.de>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Acked-by: default avatarMuli Ben-Yehuda <muli@il.ibm.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
parent 5809f9d4

Documentation/kernel-parameters.txt

+3 −0
Original line number Diff line number Diff line
@@ -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

Documentation/x86_64/boot-options.txt

+75 −34
Original line number Diff line number Diff line
@@ -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=[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

IOMMU (input/output memory management unit)



 Currently four x86-64 PCI-DMA mapping implementations exist:



   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"



   2. <arch/x86_64/kernel/pci-gart.c>: AMD GART based hardware IOMMU.

      Kernel boot message: "PCI-DMA: using GART IOMMU"



   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



  swiotlb=pages[,force]



  pages  Prereserve that many 128K pages for the software IO bounce buffering.

  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

arch/x86_64/Kconfig

+8 −2
Original line number Diff line number Diff line
@@ -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

arch/x86_64/kernel/pci-dma.c

+4 −24
Original line number Diff line number Diff line
@@ -223,29 +223,9 @@ 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)

{