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 13:53:14 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
CC:	"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

Pallipadi, Venkatesh wrote:
> 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

Some of them were changed, others not changed, with no explanation...
More changes 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

        PAT (please)

> +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

                              only works with IO (non-RAM)

> +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.


-- 
~Randy
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