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x86: PAT: update documentation to cover pgprot and remap_pfn related changes - v3

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Impact: Documentation only.

Add documentation related to pgprot_* change.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
venkatesh.pallipadi@intel.com 2008-12-18 11:41:33 -08:00 committed by H. Peter Anvin
parent 2520bd3123
commit a2ced6e173
1 changed files with 24 additions and 0 deletions
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Documentation/x86/pat.txt
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@ -80,6 +80,30 @@ pci proc | -- | -- | WC |
| | | |
-------------------------------------------------------------------
Advanced APIs for drivers
-------------------------
A. Exporting pages to user 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, driver 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()
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