linux-kernel - Re: [patch 7/7] x86 PAT: update documentation to cover pgprot and remap_pfn related changes

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Date:	Thu, 18 Dec 2008 13:13:28 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	venkatesh.pallipadi@...el.com
CC:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	akpm@...ux-foundation.org, npiggin@...e.de, hugh@...itas.com,
	arjan@...radead.org, jbarnes@...tuousgeek.org, rdreier@...co.com,
	jeremy@...p.org, linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [patch 7/7] x86 PAT: update documentation to cover pgprot and
 remap_pfn related changes - v3

venkatesh.pallipadi@...el.com wrote:

+Advanced APIs for drivers
+-------------------------
+A. Exporting pages to user with remap_pfn_range, io_remap_pfn_range,

                    to users
or                  to userspace

+vm_insert_pfn
+
+Drivers wanting to export some pages to userspace, do it by using mmap

Drop comma.

+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

s/pat/PAT/
s/driver/drivers/ or s/driver/a driver/

+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

                                 works with IO (non-RAM) regions. If a driver

+wants to export RAM region, it has to do set_memory_uc() or set_memory_wc()

          export a RAM region,

+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.


-- 
~Randy
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