Re: [PATCH v3] PCI: Only enable IO window if supported

[Guenter Roeck]

On 08/05/2015 09:25 PM, Yinghai Lu wrote:
> On Wed, Aug 5, 2015 at 7:22 PM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > On 08/05/2015 06:38 PM, Yinghai Lu wrote:
> > > On Wed, Aug 5, 2015 at 6:14 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> > > > It only can avoid warning with bridge, and still have warning on
> > > > devices under the bridge.
> > > >
> > > > also would have problem on transparent bridges, like
> > > >
> > > > BRIDGE_A ---- BRIDGE_AA----DEVICE_AA
> > > >                      |
> > > >                      \-- BRIDGE_AB ---DEVICE_AB
> > > >
> > > > if only BRIDGE_A and BRIDGE_AA are transparent, and BRIDGE_AB is not.
> > > >
> > > > and if pci_bridge_supports_io() return false for BRIDGE_A.
> > > >
> > > > We will have all three bridges have PCI_BUS_FLAGS_SUPPORTS_IO cleared.
> > > > so all will not been sized and will not get assigned io port resource.
> > > >
> > > > later DEVICE_AA could root bus io port as parent, and get io resource
> > > > assigned.
> > > > but DEVICE_AB will not get assigned.
> > > >
> > > > so we should get rid of pci_bridge_supports_io(), and just check root
> > > > resource IO port.
> > >
> > >
> > > I would suggest this version instead:
> > >
> > > Subject: [PATCH] PCI: Only try to assign io port only if root bus support
> > > that
> >
> > Bjorn had asked me to move the IO support check out of
> > pci_bridge_check_ranges().
> > It looks like you want to keep it there.
> >
> > Can you explain your reasons ? Sorry, I just don't understand.
>
> in pci_alloc_child_bus(), child bus's bus_flags will be assigned with
> parent's bus_flags.
>
> so if one parent bus has bridge's io bar can not changed, then all
> children bus will also
> have same bus_flags, and their bridge io bar will not used.
>
> then if BRIDGE_AB is not transparent, we do need to use it's bridge io bar.
If I understand you correctly, we might need to change the code
in pci_read_bridge_io() as follows.

> From

	if (!(child->bus_flags & PCI_BUS_FLAGS_SUPPORTS_IO))
		return;

to something like

	if (!(child->bus_flags & PCI_BUS_FLAGS_SUPPORTS_IO)) {
		if (dev->transparent)
			return;
		child->bus_flags |= PCI_BUS_FLAGS_SUPPORTS_IO;
	}

Would that solve the problem you are concerned about ?

Thanks,
Guenter

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