linux-kernel - Re: [PATCH 1/2] x86/io: add interface to reserve io memtype for a resource range. (v1.1)

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Date:   Wed, 26 Oct 2016 09:00:21 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Dave Airlie <airlied@...il.com>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Dave Airlie <airlied@...hat.com>,
        Toshi Kani <toshi.kani@...com>,
        Brian Gerst <brgerst@...il.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/2] x86/io: add interface to reserve io memtype for a
 resource range. (v1.1)

On Wed, Oct 26, 2016 at 8:12 AM, Dave Airlie <airlied@...il.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