Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 67bac792 authored by venkatesh.pallipadi@intel.com's avatar venkatesh.pallipadi@intel.com Committed by H. Peter Anvin
Browse files

x86: PAT: pfnmap documentation update changes 



Impact: Documentation only.

Documentation updates as per Randy Dunlap's comments.

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 34801ba9

Documentation/x86/pat.txt

+5 −5
Original line number Diff line number Diff line
@@ -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.