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

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Message-ID: <20090225120839.GC14279@elte.hu>
Date:	Wed, 25 Feb 2009 13:08:39 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	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
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.

Linus, do you have any preference?

	Ingo
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