linux-kernel - Re: [RFC PATCH v11 4/5] PCI / PM: Add support for the PCIe WAKE# signal for OF

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Date:   Wed, 24 Jan 2018 17:22:04 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     JeffyChen <jeffy.chen@...k-chips.com>, tony@...mide.com,
        linux-kernel@...r.kernel.org, bhelgaas@...gle.com,
        linux-pm@...r.kernel.org, shawn.lin@...k-chips.com,
        dianders@...omium.org, devicetree@...r.kernel.org,
        linux-pci@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>
Subject: Re: [RFC PATCH v11 4/5] PCI / PM: Add support for the PCIe WAKE#
 signal for OF

Hi Rafael,

Sorry once again on the delays...My email hygiene has been getting bad,
so mail gets buried.

On Fri, Jan 05, 2018 at 02:13:33AM +0100, Rafael J. Wysocki wrote:
> On Friday, January 5, 2018 1:41:31 AM CET Brian Norris wrote:
> > On Wed, Dec 27, 2017 at 01:57:07AM +0100, Rafael J. Wysocki wrote:
> > > On Tuesday, December 26, 2017 2:06:47 AM CET JeffyChen wrote:
> > > > On 12/26/2017 08:11 AM, Rafael J. Wysocki wrote:
> > > > >> >+
> > > > >> >+	dn = pci_device_to_OF_node(ppdev);
> > > > >> >+	if (!dn)
> > > > >> >+		return 0;
> > > > >> >+
> > > > >> >+	irq = of_irq_get_byname(dn, "wakeup");
> > > > > Why is this a property of the bridge and not of the device itself?
> > 
> > Wait, isn't 'dn' the port node, not the bridge node?
> 
> I may be confused about the structure you have in DT.

Probably :) And my DT structure may not be correct. But it's easily
available to review. See arch/arm64/boot/dts/rockchip/rk3399-gru.dtsi:

http://elixir.free-electrons.com/linux/v4.14.2/source/arch/arm64/boot/dts/rockchip/rk3399-gru.dtsi#L705

It has a bridge->port->device nesting hierarchy. I'm not actually sure
where this came from exactly, but I *thought* it was derived from the
standard documentation:

Documentation/devicetree/bindings/pci/pci.txt
PCI Bus Binding to: IEEE Std 1275-1994
http://www.devicetree.org/open-firmware/bindings/pci/pci2_1.pdf

I'm not so sure now...

> In the device hierarchy PCIe ports are represented as bridges.

But device hierarchy can be slightly different than DT hierarchy. In our
case, pcie@0,0 seems to correspond to the port, but has no companion
"device".

Or maybe I'm really off-base.

> > > > That is suggested by Brian, because in that way, the wakeup pin would 
> > > > not "tied to what exact device is installed (or no device, if it's a slot)."
> > 
> > I believe my thinking has evolved a bit over time, and I definitely am
> > not the one true authority on this. I'll explain my main concerns, and
> > whatever solution resolves these concerns is fine with me.
> > 
> > * I was primarily interested in avoiding handling WAKE# in the endpoint
> >   drivers (e.g., as mwifiex is today).
> 
> OK, everybody on this thread is interested in that. :-)

Sure :)

> > * I was also interested in not having to redefine a new DT device
> >   node (with new "pciABCD,1234" compatible property) for each new device
> >   attached. That just won't work for removable cards.
> 
> So if you make it the property of a bridge, it should be fine (as long
> as the bridge itself is not removable).

OK...in that case you've answered your question at the top: "Why is this
a property of the bridge and not of the device itself?" I think Jeffy
answered similarly, but this walked you through how *I* got to that
conclusion, at least.

> > I need to reread the rest of this thread a few times to really
> > understand what Rafael and Tony are discussing. But I feel like some of
> > this is still moving away from the second point above.
> > 
> > > But I don't think it works when there are two devices using different WAKE#
> > > interrupt lines under the same bridge.  Or how does it work then?
> 
> We seem to have agreed that this case needs to be neglected here.

OK, I guess that's a reasonable conclusion.

> The "wakeup-interrupt" property at the bridge level basically has to be defined
> as the wakeup interrupt for all devices on the bus under the bridge.

The only thing I'm at a loss for is whether this goes in (referring to
rk3399-gru.dtsi) &pcie or &pci_rootport. I think some versions of this
series have been aiming for the former, and some the latter.

Brian