Re: [PATCH] Add pci=assign-busses quirk to Dell Latitude D505

[Wei Yang <weiyang@linux.vnet.ibm.com>]

On Mon, Sep 15, 2014 at 01:03:19PM -0600, Bjorn Helgaas wrote:
>On Mon, Sep 15, 2014 at 05:53:05PM +0800, Wei Yang wrote:
>> On Mon, Sep 15, 2014 at 12:10:27AM +0200, Andreas Noever wrote:
>> ...
>
>> >@@ -840,8 +863,10 @@ int pci_scan_bridge(struct pci_bus *bus, struct pci_dev *dev, int max, int pass)
>> >
>> > 		if (max >= bus->busn_res.end) {
>> > 			dev_warn(&dev->dev, "can't allocate child bus %02x from %pR\n",
>> >-				 max, &bus->busn_res);
>> >-			goto out;
>> >+				 max + 1, &bus->busn_res);
>> >+			/* Try to resize bus */
>> >+			if (pci_grow_bus(bus, max + 1))
>> >+				goto out;
>> 
>> On some platforms, like powerpc, we have some limitations of the bus number a
>> bridge could have. Sometimes, we need the start bus number to be power 2
>> aligned.
>
>Huh.  I have to admit that I'm getting tired of all the powerpc-specific
>PCI hacks.  It's hard enough to get this stuff working on hardware that
>conforms to the spec, and scattering pcibios_*() hooks around makes the
>code even harder to follow.
>

Yep, those powerpc-specific things are not friendly :-(

I feel very sad it brings a lot difficulties to maintain it in linux mainline.
Sorry to bring so many trouble to you.

>What would happen if powerpc used PCI_PROBE_ONLY?  Do you really depend on
>the PCI core to configure anything for you, or does your firmware set
>everything up the way it needs to be?
>

Hmm... I had a try with PCI_PROBE_ONLY set, sounds can't bring up the machine.
Currently, we rely on the kernel to assign devices' resources. When
PCI_PROBE_ONLY is set, device resources will not be setup properly.

>Changing bridge configuration seems like something we should avoid under
>PCI_PROBE_ONLY (I haven't read Andreas' patch in detail, so I don't know if
>that's how it works).  If PCI_PROBE_ONLY would work for powerpc, then we
>wouldn't have an issue here.
>
>Bjorn

-- 
Richard Yang
Help you, Help me