linux-kernel - Re: [PATCH 08/22] swiotlb: wire up ->dma_supported in swiotlb_dma

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Message-ID: <5b14af5b-e6e9-17c5-d433-f50ccb466f90@arm.com>
Date:   Wed, 10 Jan 2018 17:23:08 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     iommu@...ts.linux-foundation.org, linux-arch@...r.kernel.org,
        linux-mips@...ux-mips.org, Michal Simek <monstr@...str.eu>,
        linux-ia64@...r.kernel.org,
        Christian König <ckoenig.leichtzumerken@...il.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Konrad Rzeszutek Wilk <konrad@...nok.org>,
        Guan Xuetao <gxt@...c.pku.edu.cn>,
        linuxppc-dev@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 08/22] swiotlb: wire up ->dma_supported in swiotlb_dma_ops

On 10/01/18 15:35, Christoph Hellwig wrote:
> On Wed, Jan 10, 2018 at 12:16:15PM +0000, Robin Murphy wrote:
>> On 10/01/18 08:09, Christoph Hellwig wrote:
>>> To properly reject too small DMA masks based on the addressability of the
>>> bounce buffer.
>>
>> I reckon this is self-evident enough that it should simply be squashed into
>> the previous patch.
> 
> x86 didn't wire it up before, so I want a clear blaimpoint for this
> change instead of mixing it up.
That almost makes sense, if x86 were using this generic swiotlb_dma_ops 
already. AFAICS it's only ia64, unicore and tile who end up using it, 
and they all had swiotlb_dma_supported hooked up to begin with. Am I 
missing something?

If regressions are going to happen, they'll surely point at whichever 
commit pulls the ops into the relevant arch code - there doesn't seem to 
be a great deal of value in having a piecemeal history of said ops 
*before* that point.

Robin.