1 files changed, 83 insertions, 49 deletions

diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index 5c86ed6f0448..625a21db0c2a 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -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
-   calgary  Use the Calgary IOMMU if it is available
-
-  swiotlb=pages[,force]
-
-  pages  Prereserve that many 128K pages for the software IO bounce buffering.
-  force  Force all IO through the software TLB.
-
-  calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
-  calgary=[translate_empty_slots]
-  calgary=[disable=<PCI bus number>]
+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 scatter-gather (SG) merging. Implies "force"
+                       (experimental).
+    nomerge            Don't do scatter-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
@@ -234,14 +275,14 @@ IOMMU
 
 Debugging
 
-  oops=panic Always panic on oopses. Default is to just kill the process,
-             but there is a small probability of deadlocking the machine.
-             This will also cause panics on machine check exceptions.
-             Useful together with panic=30 to trigger a reboot.
+  oops=panic    Always panic on oopses. Default is to just kill the process,
+                but there is a small probability of deadlocking the machine.
+                This will also cause panics on machine check exceptions.
+                Useful together with panic=30 to trigger a reboot.
 
-  kstack=N   Print that many words from the kernel stack in oops dumps.
+  kstack=N      Print N words from the kernel stack in oops dumps.
 
-  pagefaulttrace Dump all page faults. Only useful for extreme debugging
+  pagefaulttrace  Dump all page faults. Only useful for extreme debugging
                 and will create a lot of output.
 
   call_trace=[old|both|newfallback|new]
@@ -251,15 +292,8 @@ Debugging
                 newfallback: use new unwinder but fall back to old if it gets
                         stuck (default)
 
-  call_trace=[old|both|newfallback|new]
-                old: use old inexact backtracer
-                new: use new exact dwarf2 unwinder
-                both: print entries from both
-                newfallback: use new unwinder but fall back to old if it gets
-                        stuck (default)
-
-Misc
+Miscellaneous
 
   noreplacement  Don't replace instructions with more appropriate ones
                  for the CPU. This may be useful on asymmetric MP systems
-                 where some CPU have less capabilities than the others.
+                 where some CPUs have less capabilities than others.