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From: Daniel Vetter <daniel@ffwll.ch>
Date: Wed, 26 Oct 2016 09:00:21 +0200
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Subject: Re: [PATCH 1/2] x86/io: add interface to reserve io memtype for a
 resource range. (v1.1)
To: Dave Airlie <airlied@gmail.com>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>,
        Dave Airlie <airlied@redhat.com>, Toshi Kani <toshi.kani@hp.com>,
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        Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
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On Wed, Oct 26, 2016 at 8:12 AM, Dave Airlie <airlied@gmail.com> wrote:
>>> Is anything on a driver to be able to tell when this is actually needed ?
>>> How will driver developers know? Can you add a bit of documentation to
>>> the API? If its transitive towards a secondary solution indicating so
>>> would help driver developers.
>>
>> I'll plug the io-mapping stuff again here, and more specifically the
>> userspace pte wrangling stuff we've added in 4.9 to i915_mm.c. Should
>> probably move that one to the core. That way io_mapping takes care of the
>> full reservartion, and allows you to on-demand kmap (for kernel) and write
>> ptes. All nicely fast and all, and for bonus, also nicely encapsulated.
>
> Yeah I think ideally we'd want to move towards that, however we don't tend
> to want to ioremap the full range even on 64-bit, which is what io-mapping does.

Hm, I thought on 64 we have linear mappings of all the io space
anyway, and they're essentially for free. Am I wrong and there's some
overhead here too?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch