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,
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| | | |
and | | | |
MTRR says WB | | | |
| | | |
-/dev/mem | -- | -- | UC_MINUS |
+/dev/mem | -- | -- | UC- |
mmap !SYNC flag | | | |
no alias to this area | | | |
and | | | |
| | | |
-------------------------------------------------------------------
+Advanced APIs for drivers
+-------------------------
+A. Exporting pages to users with remap_pfn_range, io_remap_pfn_range,
+vm_insert_pfn
+
+Drivers wanting to export some pages to userspace do it by using mmap
+interface and a combination of
+1) pgprot_noncached()
+2) io_remap_pfn_range() or remap_pfn_range() or vm_insert_pfn()
+
+With PAT support, a new API pgprot_writecombine is being added. So, drivers can
+continue to use the above sequence, with either pgprot_noncached() or
+pgprot_writecombine() in step 1, followed by step 2.
+
+In addition, step 2 internally tracks the region as UC or WC in memtype
+list in order to ensure no conflicting mapping.
+
+Note that this set of APIs only works with IO (non RAM) regions. If driver
+wants to export a RAM region, it has to do set_memory_uc() or set_memory_wc()
+as step 0 above and also track the usage of those pages and use set_memory_wb()
+before the page is freed to free pool.
+
+
+
Notes:
-- in the above table mean "Not suggested usage for the API". Some of the --'s
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.
+
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff