linux-kernel - Re: [PATCH v2 04/10] PCI/P2PDMA: Clear ACS P2P flags for all devices behind switches

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Date:   Thu, 1 Mar 2018 12:13:10 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-block@...r.kernel.org,
        Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH v2 04/10] PCI/P2PDMA: Clear ACS P2P flags for all devices
 behind switches



On 01/03/18 11:02 AM, Bjorn Helgaas wrote:
>>   void pci_enable_acs(struct pci_dev *dev)
>>   {
>> +	if (pci_p2pdma_disable_acs(dev))
>> +		return;
> 
> This doesn't read naturally to me.  I do see that when
> CONFIG_PCI_P2PDMA is not set, pci_p2pdma_disable_acs() does nothing
> and returns 0, so we'll go ahead and try to enable ACS as before.
> 
> But I think it would be clearer to have an #ifdef CONFIG_PCI_P2PDMA
> right here so it's more obvious that we only disable ACS when it's
> selected.

I could do this... however, I wrote it this way because I've read Linus 
dislikes using #ifdef's inside function bodies and I personally agree 
with that sentiment.

Logan