Add documentation related to pgprot_* change. Signed-off-by: Venkatesh Pallipadi Signed-off-by: Suresh Siddha --- Documentation/x86/pat.txt | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) Index: linux-2.6/Documentation/x86/pat.txt =================================================================== --- linux-2.6.orig/Documentation/x86/pat.txt 2008-12-17 15:01:50.000000000 -0800 +++ linux-2.6/Documentation/x86/pat.txt 2008-12-17 17:23:16.000000000 -0800 @@ -80,6 +80,30 @@ pci proc | -- | - | | | | ------------------------------------------------------------------- +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 -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/