linux-kernel - Re: [PATCH] Add io-mapping functions to dynamically map large device apertures

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Message-ID: <20081031092125.GC14127@elte.hu>
Date:	Fri, 31 Oct 2008 10:21:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Eric Anholt <eric@...olt.net>
Cc:	linux-kernel@...r.kernel.org, Keith Packard <keithp@...thp.com>
Subject: Re: [PATCH] Add io-mapping functions to dynamically map large
	device apertures

* Eric Anholt <eric@...olt.net> wrote:

> From: Keith Packard <keithp@...thp.com>
> 
> Graphics devices have large PCI apertures which would consume a significant
> fraction of a 32-bit address space if mapped during driver initialization.
> Using ioremap at runtime is impractical as it is too slow. This new set of
> interfaces uses atomic mappings on 32-bit processors and a large static
> mapping on 64-bit processors to provide reasonable 32-bit performance and
> optimal 64-bit performance.
> 
> The current implementation sits atop the io_map_atomic fixmap-based mechanism
> for 32-bit processors.
> 
> This includes some editorial suggestions from Randy Dunlap for
> Documentation/io-mapping.txt
> 
> Signed-off-by: Keith Packard <keithp@...thp.com>
> Signed-off-by: Eric Anholt <eric@...olt.net>
> ---
>  Documentation/io-mapping.txt |   76 +++++++++++++++++++++++++++
>  include/linux/io-mapping.h   |  118 ++++++++++++++++++++++++++++++++++++++++++

I've applied your three patches to tip/core/resources for testing, 
thanks!

One small detail:

> +++ b/include/linux/io-mapping.h

> +#ifdef CONFIG_X86_64

it's ugly and inflexible to put x86 dependencies into generic headers. 
(even though with a high likelyhood 32-bit x86 will be the only arch 
to ever implement the iomap_atomic() APIs)

Instead please add a HAVE_ATOMIC_IOMAP define to arch/x86/Kconfig:

 config HAVE_ATOMIC_IOMAP
         def_bool y
         depends on X86_32

... and use #ifndef HAVE_ATOMIC_IOMAP in include/linux/io-mapping.h 
instead of #ifdef CONFIG_X86_64.

( Other 32-bit architectures which need an atomic iomap implementation
  for address space reasons can then implement the iomap_atomic*() 
  APIs too and set this same flag, to gain the same generic io_mapping
  implementation. )

Please send this cleanup as a delta patch, ontop of your three 
patches.

	Ingo
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