linux-kernel - Re: [PATCH 12/21] dma-iommu: factor atomic pool allocations into helpers

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Date:   Fri, 19 Apr 2019 11:07:59 +0200
From:   Christoph Hellwig <hch@....de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Christoph Hellwig <hch@....de>, Joerg Roedel <joro@...tes.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/21] dma-iommu: factor atomic pool allocations into
 helpers

On Thu, Apr 18, 2019 at 05:41:00PM +0100, Robin Murphy wrote:
>>  From a very high level POV this looks ok, but sometimes a bit to
>> convoluted to me.  The major issue why I went with the version I posted
>> is that I can cleanly ifdef out the remap code in just a few sections.
>> In this version it is spread out a lot more, and the use of IS_ENABLED
>> means that we'd need a lot more stubs for functionality that won't
>> ever be called but needs to be compilable.
>
> What functionality do you have planned in that regard? I did do a quick 
> build test of my arm64 config with DMA_DIRECT_REMAP hacked out, and 
> dma-iommu.o appeared to link OK (although other bits of arm64 and 
> dma-direct didn't, as expected). I will try x86 with IOMMU_DMA to make 
> sure, though.

Yeah, this seems to actually work, there just is a huge chunk of
remapping that is hopefully discarded by the compiler even without the
ifdefs.