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SubjectRe: [PATCH 09/11] swiotlb-xen: simplify cache maintainance
On 9/6/19 10:01 AM, 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().

(with corrected Juergen's email)

I know about IS_ENABLED() but I didn't realize that this is allowed for
compile-time inlines and such as well.

Anyway, for non-ARM bits

Reviewed-by: Boris Ostrovsky <>

If this goes via Xen tree then the first couple of patches need an ack
from ARM maintainers.


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