linux-kernel - Re: [PATCH v2 08/13] PCI/portdrv: Simplify PCIe feature permission checking

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Message-ID: <20180312140316.GB194000@bhelgaas-glaptop.roam.corp.google.com>
Date:   Mon, 12 Mar 2018 09:03:16 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        Keith Busch <keith.busch@...el.com>,
        Sinan Kaya <okaya@...eaurora.org>,
        Lukas Wunner <lukas@...ner.de>,
        Frederick Lawler <fred@...dlawl.com>
Subject: Re: [PATCH v2 08/13] PCI/portdrv: Simplify PCIe feature permission
 checking

On Mon, Mar 12, 2018 at 01:04:02AM -0700, Christoph Hellwig wrote:
> > +	 * We assume we can manage these PCIe features.  Some systems may
> > +	 * reserve these for use by the platform itself, e.g., an ACPI BIOS
> > +	 * may implement its own AER handling and use _OSC to prevent the
> > +	 * OS from interfering.
> > +	 */
> > +	bridge->use_aer = 1;
> > +	bridge->use_hotplug = 1;
> > +	bridge->use_pme = 1;
> 
> If we start out with enabled maybe these should be disable_foo flags
> instead?

I went back and forth on that.  "disable_foo" is nice because the
default value is correct (zero means enabled).  But then you end up
with things like:

  if (pcie_ports_native || !host->disable_hotplug)

where the "!host->disable_hotplug" is a double negative, and I have a
really hard time reading that.

> Also please use bool (or a bitfield bool) for true/false values.

I'm a little ambivalent about bool in structs because of things like
this:

  https://lkml.kernel.org/r/CA+55aFxnePDimkVKVtv3gNmRGcwc8KQ5mHYvUxY8sAQg6yvVYg@mail.gmail.com

Bjorn