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

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Date:   Thu, 18 Apr 2019 19:15:00 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     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 18/04/2019 17:35, Christoph Hellwig wrote:
> On Thu, Apr 18, 2019 at 04:06:56PM +0100, Robin Murphy wrote:
>> OK, I'm still looking at mmap and get_sgtable, but for now I've pushed out
>> a partial branch that consolidates alloc and free in a way which makes
>> sense to me:
>>
>>    git://linux-arm.org/linux-rm  dma/rework
>>
>> Please let me know what you think.
> 
>  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.

OK, for some reason I'd convinced myself that mmap and get_sgtable would 
need changes to properly handle the new non-remapped CMA case - not sure 
how I reached that conclusion. On inspection they do appear to be broken 
for the non-coherent atomic case, but AFAICS that's been so forever...

Still, I've worked in the vm_map_pages() stuff pending in MM and given 
them the same treatment to finish the picture. Both x86_64_defconfig and 
i386_defconfig do indeed compile and link fine as I expected, so I 
really would like to understand the concern around #ifdefs better.

Robin.