Commit a2ced6e1 authored by venkatesh.pallipadi@intel.com's avatar venkatesh.pallipadi@intel.com Committed by H. Peter Anvin
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x86: PAT: update documentation to cover pgprot and remap_pfn related changes - v3 



Impact: Documentation only.

Add documentation related to pgprot_* change.

Signed-off-by: default avatarVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 2520bd31

Documentation/x86/pat.txt

+24 −0
Original line number Diff line number Diff line
@@ -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