linux-kernel - Re: [PATCH 09/11] swiotlb-xen: simplify cache maintainance

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Date:   Fri, 6 Sep 2019 10:46:34 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:     Christoph Hellwig <hch@....de>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Juergen Gross <jgross@...e.com>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        xen-devel@...ts.xenproject.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/11] swiotlb-xen: simplify cache maintainance

On 9/6/19 10:43 AM, Konrad Rzeszutek Wilk wrote:
> On Fri, Sep 06, 2019 at 10:19:01AM -0400, Boris Ostrovsky wrote:
>> 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 <boris.ostrovsky@...cle.com>
> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>
> as well.
>
> Albeit folks have tested this under x86 Xen with 'swiotlb=force' right?


Yes, I did.

-boris


>
> I can test it myself but it will take a couple of days.
>> If this goes via Xen tree then the first couple of patches need an ack
>> from ARM maintainers.
>>
>> -boris