Re: [PATCH] SB600 for the Nemo board has non-zero devices on non-root bus

From: Bjorn Helgaas <helgaas@kernel.org>
To: Christian Zigotzky <chzigotzky@xenosoft.de>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	linux-pci@vger.kernel.org
Subject: Re: [PATCH] SB600 for the Nemo board has non-zero devices on non-root bus
Date: Fri, 1 Dec 2017 17:27:16 -0600	[thread overview]
Message-ID: <20171201232716.GA18780@bhelgaas-glaptop.roam.corp.google.com> (raw)
In-Reply-To: <406ba7c4-7305-4069-227f-81afed202e47@xenosoft.de>

On Fri, Dec 01, 2017 at 11:08:46PM +0100, Christian Zigotzky wrote:
> On 30.11.2017 23:42, Bjorn Helgaas wrote:
> >
> > 00:11.0 claims to be a PCIe Root Port leading to [bus 05-06]. That
> > means there's a Link (presumably this A-Link II Express thing), and the
> > downstream end of the Link *should* be a PCIe Upstream Port on bus 05,
> > but no such device is visible.  I suppose the SB600 does implement
> > some sort of PCIe Port there, but keeps it invisible to software, and
> > at the same time, contains an invisible bridge that connects the Link
> > to all the conventional PCI devices on bus 05.
> >
> > When we scan bus 05, we do this:
> >
> >   pci_scan_child_bus_extend(bus=05)
> >     for (devfn = 0; devfn < 0x100; devfn += 8)
> >       pci_scan_slot(05, 00.0)
> >         pci_scan_single_device
> >           pci_scan_device(05, 00.0)           # fails; no 05:00.0
> >       pci_scan_slot(05, 01.0)
> >         only_one_child(bus=05)
> >           parent = 00:11.0
> >           pci_pcie_type(00:11.0) == ROOT_PORT # returns true
> >
> > Since only_one_child() sees that 00:11.0 is a Root Port, we give up
> > before we even get to the PCI_SCAN_ALL_PCIE_DEVS test.
> >
> > I *think* something like the patch below should make this work if you
> > use the "pci=pcie_scan_all" parameter.  We have some x86 DMI quirks
> > that set PCI_SCAN_ALL_PCIE_DEVS automatically.  I don't know how to do
> > something similar on powerpc, but maybe you do?
> >
> 
> Hi Bjorn,
> 
> I tested your new patch today. It boots with the boot argument
> "pci=pcie_scan_all". Well done! :-)
> 
> It doesn't boot without the boot argument "pci=pcie_scan_all".

Thanks for testing that.  I'll merge a similar patch for v4.16.

I don't think using "pci=pcie_scan_all" is really an acceptable
long-term answer for you, though.  Is there some way we can identify
at run-time whether we're on a Nemo system?  If so, we can make this
happen automatically.

Bjorn