Date:   Tue, 24 Oct 2017 15:10:00 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Jeffy Chen <jeffy.chen@...k-chips.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org, shawn.lin@...k-chips.com,
        dianders@...omium.org, linux-pci@...r.kernel.org,
        linux-pm@...r.kernel.org, Tony Lindgren <tony@...mide.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v7 1/3] PCI: Add support for wake irq

Include "PCIe WAKE#" signal in the subject, since this is specifically
about that wire.

On Mon, Oct 23, 2017 at 04:02:53PM -0700, Brian Norris wrote:
> + PM folks
> 
> Hi Jeffy,
> 
> It's probably good if you send the whole thing to linux-pm@ in the
> future, if you're really trying to implement generic PCI/PM for device
> tree systems.
> 
> On Thu, Oct 19, 2017 at 07:10:05PM +0800, Jeffy Chen wrote:
> > Add support for PCIE_WAKE pin.

I think you're referring to what the spec calls "the WAKE# signal".
It will reduce confusion if you use exactly the same notation as the
spec.

> This is kind of an important change, so it feels like you should
> document it a little more thoroughly than this. Particularly, I have a
> few questions below, and it seems like some of these questions should be
> acknowledged up front. e.g., why does this look so different than the
> ACPI hooks?
> 
> > 
> > Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> > ---
> > 
> > Changes in v7:
> > Move PCIE_WAKE handling into pci core.
> > 
> > Changes in v6:
> > Fix device_init_wake error handling, and add some comments.
> > 
> > Changes in v5:
> > Rebase
> > 
> > Changes in v3:
> > Fix error handling
> > 
> > Changes in v2:
> > Use dev_pm_set_dedicated_wake_irq
> >         -- Suggested by Brian Norris <briannorris@...omium.com>
> > 
> >  drivers/pci/pci.c    | 34 ++++++++++++++++++++++++++++++++--
> >  drivers/pci/probe.c  | 32 ++++++++++++++++++++++++++++----
> >  drivers/pci/remove.c |  9 +++++++++
> >  3 files changed, 69 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index f0d68066c726..49080a10bdf0 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -603,10 +603,40 @@ static inline pci_power_t platform_pci_choose_state(struct pci_dev *dev)
> >  			pci_platform_pm->choose_state(dev) : PCI_POWER_ERROR;
> >  }
> >  
> > +static int pci_dev_check_wakeup(struct pci_dev *dev, void *data)
> > +{
> > +	bool *wakeup = data;
> > +
> > +	if (device_may_wakeup(&dev->dev))
> > +		*wakeup = true;
> > +
> > +	return *wakeup;
> > +}
> > +
> >  static inline int platform_pci_set_wakeup(struct pci_dev *dev, bool enable)
> >  {
> > -	return pci_platform_pm ?
> > -			pci_platform_pm->set_wakeup(dev, enable) : -ENODEV;
> > +	struct pci_dev *parent = dev;
> > +	struct pci_bus *bus;
> > +	bool wakeup = false;
> 
> It feels like you're implementing a set of pci_platform_pm_ops, except
> you're not actually implementing them. It almost seems like we should
> have a drivers/pci/pci-of.c to do this. But that brings up a few
> questions....
> 
> > +
> > +	if (pci_platform_pm)
> 
> So, if somebody already registered ops, then you won't follow the "OF"
> route? That means this all breaks as soon as a kernel has both
> CONFIG_ACPI and CONFIG_OF enabled. This is possible on at least ARM64,
> which 'select's OF and may also be built/run with CONFIG_ACPI.
> 
> And that conflict is the same if we try to register pci_platform_pm_ops
> for OF systems -- it'll be a race over who sets them up first (or
> rather, last).
> 
> Also, what happens on !ACPI && !OF? Or if the device tree did not
> contain a "wakeup" definition? You're now implementing a default path
> that doesn't make much sense IMO; you may claim wakeup capability
> without actually having set it up somewhere.
> 
> I think you could use some more comments, and (again) a real commit
> message.
> 
> > +		return pci_platform_pm->set_wakeup(dev, enable);
> > +
> > +	device_set_wakeup_capable(&dev->dev, enable);
> 
> Why are you setting that here? This function should just be telling the
> lower layers to enable the physical WAKE# ability. In our case, it just
> means configuring the WAKE# interrupt for wakeup -- or, since you've
> used dev_pm_set_dedicated_wake_irq() which handles most of this
> automatically...do you need this at all? It seems like you should
> *either* implement these callbacks to manually manage the wakeup IRQ or
> else use the dedicated wakeirq infrastructure -- not both.
> 
> And even if you need this, I don't think you need to do this many times;
> you should only need to set up the capabilities once, when you first set
> up the device.
> 
> And BTW, the description for the set_wakeup() callback says:
> 
>  * @set_wakeup: enables/disables wakeup capability for the device
> 
> I *don't* think that means "capability" as in the device framework's
> view of "wakeup capable"; I think it means capability as in the physical
> ability (a la, enable_irq_wake() or similar).
> 
> > +
> > +	while ((parent = pci_upstream_bridge(parent)))
> > +		bus = parent->bus;
> > +
> > +	if (!bus || !pci_is_root_bus(bus) || !bus->bridge->parent)
> > +		return -ENODEV;
> > +
> > +	pci_walk_bus(bus, pci_dev_check_wakeup, &wakeup);
> > +	device_set_wakeup_capable(bus->bridge->parent, wakeup);
> 
> What happens to any intermediate buses? You haven't marked them as
> wakeup-capable. Should you?
> 
> And the more fundamental question here is: is this a per-device
> configuration or a per-root-port configuration? The APIs here are
> modeled after ACPI, where I guess this is a per-device thing. The PCIe
> spec doesn't exactly specify how many WAKE# pins you need, though it
> seems to say
> 
> (a) it's all-or-nothing (if one device uses it, all wakeup-capable EPs
>     should be wired up to it)
> (b) it *can* be done as a single input to the system controller, since
>     it's an open drain signal
> (c) ...but I also see now in the PCIe Card Electromechanical
>     specification:
> 
>     "WAKE# may be bused to multiple PCI Express add-in card connectors,
>     forming a single input connection at the PM controller, or
>     individual connectors can have individual connections to the PM
>     controller."
> 
> So I think you're kind of going along the lines of (b) (as I suggested
> to you previously), and that matches the current hardware (we only have
> a single WAKE#) and proposed DT binding. But should this be set up in a
> way that suits (c) too? It's hard to tell exactly what ACPI-based
> systems do, since they have this abstracted behind ACPI interfaces that
> seem like they *could* support per-device or per-bridge type of hookups.
> 
> Bjorn, any thoughts? This seems like a halfway attempt in between two
> different designs, and I'm not really sure which one makes more sense.

No thoughts yet.  Seems like this needs a little more time in the
oven, and I'll take a deeper look after some of the issues you pointed
out have been addressed.

Bjorn

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