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authorvenkatesh.pallipadi@intel.com <venkatesh.pallipadi@intel.com>2008-12-18 11:41:33 -0800
committerH. Peter Anvin <hpa@zytor.com>2008-12-18 13:30:16 -0800
commita2ced6e173e0c93870f79856e97825f4e180891e (patch)
treec0bc36dcc594197f392f82f2cca36167ff9584e4 /Documentation/x86/pat.txt
parent2520bd3123c00272f818a176c92d03c7d0a113d6 (diff)
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: 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>
Diffstat (limited to 'Documentation/x86/pat.txt')
-rw-r--r--Documentation/x86/pat.txt24
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt
index c93ff5f4c0dd..1784ff276997 100644
--- a/Documentation/x86/pat.txt
+++ b/Documentation/x86/pat.txt
@@ -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

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