linux-kernel - Re: [PATCH v2] PCI hotplug Eq v2

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Message-ID: <20180917205354.GB54859@bhelgaas-glaptop.roam.corp.google.com>
Date:   Mon, 17 Sep 2018 15:53:54 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Jon Derrick <jonathan.derrick@...el.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Keith Busch <keith.busch@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Sinan Kaya <okaya@...nel.org>, Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH v2] PCI hotplug Eq v2

On Thu, Aug 30, 2018 at 04:11:59PM -0600, Jon Derrick wrote:
> Hi Bjorn,
> 
> Sorry for the delay on this one and pushing it after RC1.
> Feel free to queue it up for 4.20 if it looks fine.
> 
> I've added comments to the git log and source explaining why
> calculate_iosize was left unchanged. Basically I could not
> synthesize a condition where it would have affected the topology.

In other words, the only reason you didn't change the
calculate_iosize() path was because you couldn't test it?

I appreciate your desire to avoid untested changes, but I think it's
very important to preserve and even improve the symmetry between
calculate_memsize() and calculate_iosize().  For example, it's not
obvious why the order is different here:

  calculate_iosize():
    size = ALIGN(size + size1, align);
    if (size < old_size)
      size = old_size;

  calculate_memsize():
    if (size < old_size)
      size = old_size;
    size = ALIGN(size + size1, align);

So I don't want to diverge them further unless there's a real
functional reason why we need to handle I/O port space differently
than MMIO space.

You've tested the MMIO path, and I'm willing to take the risk of
doing the same thing in the I/O port path.

Bjorn