linux-kernel - RE: [patch 0/4] gpu/drm, x86, PAT: Add PAT support for io_mapping

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Date:	Wed, 25 Feb 2009 06:06:59 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Dave Airlie <airlied@...hat.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Eric Anholt <eric@...olt.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	Keith Packard <keithp@...thp.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [patch 0/4] gpu/drm, x86, PAT: Add PAT support for	io_mapping_*
 interface

 

>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@...e.hu] 
>Sent: Wednesday, February 25, 2009 4:09 AM
>To: Pallipadi, Venkatesh; Linus Torvalds
>Cc: Dave Airlie; Jesse Barnes; Eric Anholt; Thomas Gleixner; H 
>Peter Anvin; Keith Packard; linux-kernel@...r.kernel.org
>Subject: Re: [patch 0/4] gpu/drm, x86, PAT: Add PAT support 
>for io_mapping_* interface
>
>
>* Venkatesh Pallipadi <venkatesh.pallipadi@...el.com> wrote:
>
>> io_mapping_create_wc(), io_mapping_free() and associated 
>map/unmap routines
>> are relatively new set of APIs for drivers, that change memory type.
>> 
>> Currently, these interfaces hardcode WC type on x86 and does 
>not go through
>> "PAT enforcement". This patchset adds PAT support for this interface.
>> 
>> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
>> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
>
>hm, the patches look sane and clean and mostly factor out 
>existing code and checks and apply them to the io_mapping_*() 
>interfaces - so it's something worth having for .29.
>
>But it's all rather awfully late in the cycle and ioremap type 
>of bugs typically have 1-2 rc's of latency to be fully 
>discovered.
>
>They will probably fix a few regressions and are easy to revert, 
>plus they affect the one driver whose authors wrote these 
>facilities:
>
>  drivers/gpu/drm/i915/i915_dma.c
>  drivers/gpu/drm/i915/i915_gem.c
>
>so maybe we should try it as it's all a clear step forward. I'll 
>give them a spin in tip:x86/urgent. Dunno.
>

Actual PAT support (patch 3 and 4) can probably wait until .30. As
there is only one user of this interface. Patch 1 and 2 are more in
bugfix category and probably considered for .29.

Thanks,
Venki--
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