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

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Message-ID: <20081218214940.GA31088@linux-os.sc.intel.com>
Date:	Thu, 18 Dec 2008 13:49:41 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"npiggin@...e.de" <npiggin@...e.de>,
	"hugh@...itas.com" <hugh@...itas.com>,
	"arjan@...radead.org" <arjan@...radead.org>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"rdreier@...co.com" <rdreier@...co.com>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Subject: Re: [patch 7/7] x86 PAT: update documentation to cover pgprot and remap_pfn related changes - v3

On Thu, Dec 18, 2008 at 01:13:28PM -0800, Randy Dunlap wrote:
> 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.
> 
> 

refreshed patch below

Thanks,
Venki


Add documentation related to pgprot_* change.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
---
 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 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
+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, 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 a 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.
+
+
+
 Notes:
 
 -- in the above table mean "Not suggested usage for the API". Some of the --'s
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