Re: [RFC/RFT PATCH v2] PCI: move pci_read_bridge_bases to the generic PCI layer

[Guenter Roeck]

On 06/13/2015 02:12 AM, Lorenzo Pieralisi wrote:
> On Sat, Jun 13, 2015 at 02:47:55AM +0100, Guenter Roeck wrote:
> > On Tue, Jun 09, 2015 at 10:01:45AM +0100, Lorenzo Pieralisi wrote:
> > > When a PCI bus is scanned, upon PCI bridge detection the kernel
> > > has to read the bridge registers to set-up its resources so that
> > > the PCI resource hierarchy can be validated properly.
> > >
> > > Most if not all architectures read PCI bridge registers in the
> > > pcibios_fixup_bus hook, that is called by the PCI generic layer
> > > whenever a PCI bus is scanned.
> > >
> > > Since pci_read_bridge_bases is an arch agnostic operation (and it
> > > is carried out on all architectures) it can be moved to the generic
> > > PCI layer in order to consolidate code and remove the respective
> > > calls from the architectures back-ends.
> > >
> > > The PCI_PROBE_ONLY flag is not checked before calling
> > > pci_read_bridge_buses in the generic layer since reading the bridge
> > > bases is not related to resources assignment; this implies that it
> > > can be carried out safely on PCI_PROBE_ONLY systems too and should
> > > not affect architectures (alpha, mips) that check the PCI_PROBE_ONLY
> > > flag before reading the bridge bases.
> > >
> > > In order to validate the resource hierarchy as soon as the resources
> > > themselves are probed (ie read from the bridge), this patch also adds
> > > code to pci_read_bridge_bases that claims the bridge resources, so that
> > > they are validated and inserted in the resource hierarchy as soon as
> > > the bridge bases are probed.
> >
> > Hi Lorenzo,
> >
> > on one of our systems, I see a lot of messages with your patch applied.
> >
> > bart kernel: pci 0000:b0:00.0: can't claim BAR 7 [io 0x0000-0x0fff]: no compatible bridge window
> > bart kernel: pci 0000:b0:00.0: can't claim BAR 8 [mem 0x94000000-0x941fffff]: no compatible bridge window
> > bart kernel: pci 0000:b1:03.0: can't claim BAR 7 [io 0x0000-0x0fff]: no compatible bridge window
> > bart kernel: pci 0000:b1:03.0: can't claim BAR 8 [mem 0x95800000-0x959fffff]: no compatible bridge window
> >
> > and so on. The final IO memory assignment is the same, though,
> > before and after your patch.
> >
> >        95800000-95bfffff : PCI Bus 0000:b0
> >          95800000-959fffff : PCI Bus 0000:b1
> > 	  95800000-959fffff : PCI Bus 0000:b2
> > 	95a00000-95a3ffff : 0000:b0:00.0
> >
> >
> > Does that have any relevance or is it just nuisance messages ?
>
> Yes, I knew this could happen. It should be just nuisance messages,
> since we are claming bridge resources even on systems where they
> are reassigned. We should remove those messages, this means that I
> have to craft a function that claims resources without spitting too
> much unwanted noise, I can't use pci_claim_bridge_resource for this
> purpose as you have noticed, unless I refactor it, open to suggestions
> (we claim bridge resources by default, regardless of PROBE_ONLY flag).
>
> Thanks a lot for testing it, appreciated, I will prepare a v3.

Hi Lorenzo,

There is no need for v3 because of this. My patch set addresses the BAR 7
message, and the BAR 8 message is actually warranted since the memory
window on the upstream port is too small.

Guenter

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/