On Sun, Jun 14, 2015 at 04:29:52PM +0100, Guenter Roeck wrote: > 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.
I'd agree it is warranted, still we have to expect similar messages printed on kernel logs for other platforms that are _not_ printed by current mainline, I guess that's acceptable and it was expected when we decided to claim bridge resources in core code by default. I am open to feedback if we want to change this behaviour, I am more concerned about the patch test coverage to check it does not affect behaviour on archs we do not have HW to test on. Thank you, Lorenzo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
