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| -rw-r--r-- | Documentation/x86/pat.txt | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt index c93ff5f4c0d..1784ff27699 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 |