linux-kernel - Re: [PATCH 02/19] dma-iommu: cleanup dma-iommu.h

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Date:   Wed, 6 Feb 2019 15:08:26 +0000
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 02/19] dma-iommu: cleanup dma-iommu.h

On 01/02/2019 16:13, Christoph Hellwig wrote:
> On Fri, Feb 01, 2019 at 02:47:17PM +0000, Robin Murphy wrote:
>> On 14/01/2019 09:41, Christoph Hellwig wrote:
>>> No need for a __KERNEL__ guard outside uapi, make sure we pull in the
>>> includes unconditionally so users can rely on it, and add a missing
>>> comment describing the #else cpp statement.  Last but not least include
>>> <linux/errno.h> instead of the asm version, which is frowned upon.
>>
>> I think the __KERNEL__ and asm/errno.h slip-ups are things I cargo-culted
>> from the arch code as a fresh-faced noob yet to learn the finer details, so
>> ack for those parts. The forward-declarations, though, were a deliberate
>> effort to minimise header dependencies and compilation bloat for includers
>> who absolutely wouldn't care, and specifically to try to avoid setting
>> transitive include expectations since they always seem to end up breaking
>> someone's config somewhere down the line. Admittedly this little backwater
>> is hardly comparable to the likes of the sched.h business, but I'm still
>> somewhat on the fence about that change :/
> 
> As far as I can tell almost all users of linux/dma-iommu.h require
> CONFIG_DMA_IOMMU to be enabled anyway..

Other than dma-iommu.c itself, none of them *require* it - only 
arch/arm64 selects it (the one from MTK_IOMMU is just bogus), and a lot 
of the drivers also build for at least one other architecture (and/or 
arm64 with !IOMMU_API).

Either way, I have no vehement objection to the change, I just don't see 
any positive value in it.

Robin.