Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Received-SPF: None (esa5.hc3370-68.iphmx.com: no sender
  authenticity information available from domain of
  andrew.cooper3@citrix.com) identity=pra;
  client-ip=162.221.158.21; receiver=esa5.hc3370-68.iphmx.com;
  envelope-from="Andrew.Cooper3@citrix.com";
  x-sender="andrew.cooper3@citrix.com";
  x-conformance=sidf_compatible
Received-SPF: Pass (esa5.hc3370-68.iphmx.com: domain of
  Andrew.Cooper3@citrix.com designates 162.221.158.21 as
  permitted sender) identity=mailfrom;
  client-ip=162.221.158.21; receiver=esa5.hc3370-68.iphmx.com;
  envelope-from="Andrew.Cooper3@citrix.com";
  x-sender="Andrew.Cooper3@citrix.com";
  x-conformance=sidf_compatible; x-record-type="v=spf1";
  x-record-text="v=spf1 ip4:209.167.231.154 ip4:178.63.86.133
  ip4:195.66.111.40/30 ip4:85.115.9.32/28 ip4:199.102.83.4
  ip4:192.28.146.160 ip4:192.28.146.107 ip4:216.52.6.88
  ip4:216.52.6.188 ip4:162.221.158.21 ip4:162.221.156.83 ~all"
Received-SPF: None (esa5.hc3370-68.iphmx.com: no sender
  authenticity information available from domain of
  postmaster@mail.citrix.com) identity=helo;
  client-ip=162.221.158.21; receiver=esa5.hc3370-68.iphmx.com;
  envelope-from="Andrew.Cooper3@citrix.com";
  x-sender="postmaster@mail.citrix.com";
  x-conformance=sidf_compatible
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 Qow=
Subject: Re: [Xen-devel] [PATCH 09/11] swiotlb-xen: simplify cache
 maintainance
To:     Christoph Hellwig <hch@lst.de>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC:     Stefano Stabellini <sstabellini@kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        <x86@kernel.org>, <linux-kernel@vger.kernel.org>,
        <iommu@lists.linux-foundation.org>, <gross@suse.com>,
        <xen-devel@lists.xenproject.org>,
        <linux-arm-kernel@lists.infradead.org>
References: <20190905113408.3104-1-hch@lst.de>
 <20190905113408.3104-10-hch@lst.de>
 <e4f9b393-2631-57cd-f42f-3581e75ab9a3@oracle.com>
 <20190906140123.GA9894@lst.de>
From:   Andrew Cooper <andrew.cooper3@citrix.com>
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Message-ID: <a42a1ae5-6181-ee65-17a8-32eb0e702901@citrix.com>
Date:   Fri, 6 Sep 2019 15:07:42 +0100
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Precedence: bulk

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