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Commit 59dfc3f8 authored by venkatesh.pallipadi@intel.com's avatar venkatesh.pallipadi@intel.com Committed by Ingo Molnar
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x86: PAT documentation updates with debug info 



Documentation update for PAT. Reflect the latest API details.
Also, adds details about ways to get more info in order to debug PAT.

Signed-off-by: default avatarVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 470fba7e

Documentation/x86/pat.txt

+45 −9
Original line number Diff line number Diff line
@@ -14,6 +14,10 @@ PAT allows for different types of memory attributes. The most commonly used 
ones that will be supported at this time are Write-back, Uncached,

Write-combined and Uncached Minus.





PAT APIs

--------



There are many different APIs in the kernel that allows setting of memory

attributes at the page level. In order to avoid aliasing, these interfaces

should be used thoughtfully. Below is a table of interfaces available,
@@ -26,38 +30,38 @@ address range to avoid any aliasing. 
API                    |    RAM   |  ACPI,...  |  Reserved/Holes  |

-----------------------|----------|------------|------------------|

                       |          |            |                  |

ioremap                |    --    |    UC      |       UC         |

ioremap                |    --    |    UC-     |       UC-        |

                       |          |            |                  |

ioremap_cache          |    --    |    WB      |       WB         |

                       |          |            |                  |

ioremap_nocache        |    --    |    UC      |       UC         |

ioremap_nocache        |    --    |    UC-     |       UC-        |

                       |          |            |                  |

ioremap_wc             |    --    |    --      |       WC         |

                       |          |            |                  |

set_memory_uc          |    UC    |    --      |       --         |

set_memory_uc          |    UC-   |    --      |       --         |

 set_memory_wb         |          |            |                  |

                       |          |            |                  |

set_memory_wc          |    WC    |    --      |       --         |

 set_memory_wb         |          |            |                  |

                       |          |            |                  |

pci sysfs resource     |    --    |    --      |       UC         |

pci sysfs resource     |    --    |    --      |       UC-        |

                       |          |            |                  |

pci sysfs resource_wc  |    --    |    --      |       WC         |

 is IORESOURCE_PREFETCH|          |            |                  |

                       |          |            |                  |

pci proc               |    --    |    --      |       UC         |

pci proc               |    --    |    --      |       UC-        |

 !PCIIOC_WRITE_COMBINE |          |            |                  |

                       |          |            |                  |

pci proc               |    --    |    --      |       WC         |

 PCIIOC_WRITE_COMBINE  |          |            |                  |

                       |          |            |                  |

/dev/mem               |    --    |    UC      |       UC         |

/dev/mem               |    --    |  WB/WC/UC- |    WB/WC/UC-     |

 read-write            |          |            |                  |

                       |          |            |                  |

/dev/mem               |    --    |    UC      |       UC         |

/dev/mem               |    --    |    UC-     |       UC-        |

 mmap SYNC flag        |          |            |                  |

                       |          |            |                  |

/dev/mem               |    --    |  WB/WC/UC  |    WB/WC/UC      |

/dev/mem               |    --    |  WB/WC/UC- |    WB/WC/UC-     |

 mmap !SYNC flag       |          |(from exist-|  (from exist-    |

 and                   |          |  ing alias)|    ing alias)    |

 any alias to this area|          |            |                  |
@@ -68,7 +72,7 @@ pci proc | -- | -- | WC | 
 and                   |          |            |                  |

 MTRR says WB          |          |            |                  |

                       |          |            |                  |

/dev/mem               |    --    |    --      |    UC_MINUS      |

/dev/mem               |    --    |    --      |       UC-        |

 mmap !SYNC flag       |          |            |                  |

 no alias to this area |          |            |                  |

 and                   |          |            |                  |
@@ -98,3 +102,35 @@ types. 


Drivers should use set_memory_[uc|wc] to set access type for RAM ranges.





PAT debugging

-------------



With CONFIG_DEBUG_FS enabled, PAT memtype list can be examined by



# mount -t debugfs debugfs /sys/kernel/debug

# cat /sys/kernel/debug/x86/pat_memtype_list

PAT memtype list:

uncached-minus @ 0x7fadf000-0x7fae0000

uncached-minus @ 0x7fb19000-0x7fb1a000

uncached-minus @ 0x7fb1a000-0x7fb1b000

uncached-minus @ 0x7fb1b000-0x7fb1c000

uncached-minus @ 0x7fb1c000-0x7fb1d000

uncached-minus @ 0x7fb1d000-0x7fb1e000

uncached-minus @ 0x7fb1e000-0x7fb25000

uncached-minus @ 0x7fb25000-0x7fb26000

uncached-minus @ 0x7fb26000-0x7fb27000

uncached-minus @ 0x7fb27000-0x7fb28000

uncached-minus @ 0x7fb28000-0x7fb2e000

uncached-minus @ 0x7fb2e000-0x7fb2f000

uncached-minus @ 0x7fb2f000-0x7fb30000

uncached-minus @ 0x7fb31000-0x7fb32000

uncached-minus @ 0x80000000-0x90000000



This list shows physical address ranges and various PAT settings used to

access those physical address ranges.



Another, more verbose way of getting PAT related debug messages is with

"debugpat" boot parameter. With this parameter, various debug messages are

printed to dmesg log.