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Re: [Xen-devel] [PATCH 09/11] swiotlb-xen: simplify cache maintainance


  • To: Christoph Hellwig <hch@xxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Fri, 6 Sep 2019 15:07:42 +0100
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  • Cc: x86@xxxxxxxxxx, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, gross@xxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Fri, 06 Sep 2019 14:08:17 +0000
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On 06/09/2019 15:01, Christoph Hellwig wrote:
> On Fri, Sep 06, 2019 at 09:52:12AM -0400, Boris Ostrovsky wrote:
>> We need nop definitions of these two for x86.
>>
>> Everything builds now but that's probably because the calls are under
>> 'if (!dev_is_dma_coherent(dev))' which is always false so compiler
>> optimized is out. I don't think we should rely on that.
> That is how a lot of the kernel works.  Provide protypes only for code
> that is semantically compiled, but can't ever be called due to
> IS_ENABLED() checks.  It took me a while to get used to it, but it
> actually is pretty nice as the linker does the work for you to check
> that it really is never called.  Much better than say a BUILD_BUG_ON().

Yeah - its a weird concept to get used to, but it results in much
clearer code.

~Andrew

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