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

[Guenter Roeck <linux@roeck-us.net>]

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 ?

Thanks,
Guenter