Skip to content

Commit

Permalink
x86: PAT documentation updates with debug info
Browse files Browse the repository at this point in the history 
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: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
  • Loading branch information
venkatesh.pallipadi@intel.com authored and Ingo Molnar committed Aug 21, 2008
1 parent 470fba7 commit 59dfc3f
Showing 1 changed file with 45 additions and 9 deletions.
54 changes: 45 additions & 9 deletions Documentation/x86/pat.txt
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand All @@ -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| | | |
Expand All @@ -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 | | | |
Expand Down Expand Up @@ -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.

0 comments on commit 59dfc3f

Please sign in to comment.