linux-kernel - Re: [RFC PATCH v12 1/5] dt-bindings: PCI: Add definition of PCIe WAKE# irq and PCI irq

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Date:   Sat, 30 Dec 2017 01:31:14 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Jeffy Chen <jeffy.chen@...k-chips.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Brian Norris <briannorris@...omium.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Doug Anderson <dianders@...omium.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [RFC PATCH v12 1/5] dt-bindings: PCI: Add definition of PCIe
 WAKE# irq and PCI irq

On Sat, Dec 30, 2017 at 12:50 AM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> On Fri, Dec 29, 2017 at 6:57 PM, Tony Lindgren <tony@...mide.com> wrote:
>> * Jeffy Chen <jeffy.chen@...k-chips.com> [171226 02:11]:
>>> We are going to handle PCIe WAKE# pin for PCI devices in the pci core,
>>> so add definitions of the optional PCIe WAKE# pin for PCI devices.
>>>
>>> Also add an definition of the optional PCI interrupt pin for PCI
>>> devices to distinguish it from the PCIe WAKE# pin.
>>
>>> --- a/Documentation/devicetree/bindings/pci/pci.txt
>>> +++ b/Documentation/devicetree/bindings/pci/pci.txt
>>> @@ -24,3 +24,13 @@ driver implementation may support the following properties:
>>>     unsupported link speed, for instance, trying to do training for
>>>     unsupported link speed, etc.  Must be '4' for gen4, '3' for gen3, '2'
>>>     for gen2, and '1' for gen1. Any other values are invalid.
>>> +
>>> +PCI devices may support the following properties:
>>
>> This should say PCI ports instead of PCI devices.
>
> No, it is more accurate to say "PCI devices".
>
> Well, it actually gets somewhat confusing, because in the PCI
> terminology a "PCI device" means a physical piece of hardware that can
> be put into a single "slot" (think socket on a board) and may consist
> up to 8 functional units called "functions" which are each represented
> by a struct pci_dev.  So there may be up to 8 struct pci_dev objects
> per "PCI device" (as per the standard language) and, BTW, drivers bind
> to functions (via the struct pci_dev objects).
>
> Now, WAKE# is shared by all functions within the same "PCI device"
> (I'm not sure if the standard specifies that directly, but at least it
> appears to be treated as an obvious physical limitation), so it may be
> useful to represent the "slot" or "device" level in the DT even though
> it has no struct device based representation in the kernel.

Within the convention that bridges represent "everything below them"
as far as WAKE# is concerned, it can say "The following properties may
be provided for PCI bridges:" and the description below should explain
the convention.

Thanks,
Rafael