linux-kernel - Re: [RFC PATCH 4/5] iommu/dma: Export non-static functions to use in modules

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Date:   Thu, 6 Jul 2017 23:24:28 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Robin Murphy <robin.murphy@....com>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Will Deacon <will.deacon@....com>,
        Vineet Gupta <vgupta@...opsys.com>,
        Hans-Christian Noren Egtvedt <egtvedt@...fundet.no>,
        Mitchel Humpherys <mitchelh@...eaurora.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC PATCH 4/5] iommu/dma: Export non-static functions to use in modules

On Thu, Jul 6, 2017 at 11:17 PM, Tomasz Figa <tfiga@...omium.org> wrote:
> On Thu, Jul 6, 2017 at 11:10 PM, Christoph Hellwig <hch@....de> wrote:
>> On Thu, Jul 06, 2017 at 12:09:45PM +0100, Robin Murphy wrote:
>>> I suppose another option is to just make the IOMMU and DMA ops a
>>> self-contained non-modular driver mirroring the VT-d/AMD-Vi IOMMUs -
>>> AFAICS it shouldn't have to be all that tightly coupled to the IPU bus
>>> code, the latter more or less just needs to create the appropriate IOMMU
>>> device for the driver to find.
>>
>> I still haven't seen the driver code, but this seems to be best
>> solution so far.  Given that it's not a plug in device but part of
>> an SOC that seems perfectly acceptable to me.
>
> I guess that's something that could work. With its caveats of not
> being able to avoid including the very platform specific code in a
> generic kernel image or do any quick testing of code changes without a
> restart, but I guess that's something one could quickly hack in their
> own downstream (i.e. export the symbols and turn the Kconfig entry
> into tristate).
>
> On the other hand, I'm yet to see any real reasons why not to export
> those symbols. Personally I don't see anything that one wouldn't be
> able to do in their downstream without the symbols exported in
> mainline (one can add the exports any time or if the kernel source
> can't be modified can just load a wrapper module that exports its own
> symbols...)

Sorry, I just realized that last sentence might sound nonsense. By
wrapper I meant reimplementing the missing functions using some
already exported functions I mentioned in my post to another patch
from this series, such as __get_vm_area() and map_vm_area().