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x86: PAT: pfnmap documentation update changes

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Impact: Documentation only.

Documentation updates as per Randy Dunlap's comments.

Signed-off-by: Venkatesh Pallipadi <[email protected]>
Signed-off-by: Suresh Siddha <[email protected]>
Signed-off-by: H. Peter Anvin <[email protected]>
This commit is contained in:
[email protected] 2008-12-19 13:47:30 -08:00 • committed by H. Peter Anvin
commit 67bac792cd
1 changed files with 5 additions and 5 deletions
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10
Documentation/x86/pat.txt
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@ -82,23 +82,23 @@ pci proc | -- | -- | WC |
Advanced APIs for drivers
-------------------------
A. Exporting pages to user with remap_pfn_range, io_remap_pfn_range,
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
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, driver can
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 work with IO (non RAM) regions. If driver
wants to export RAM region, it has to do set_memory_uc() or set_memory_wc()
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.