On Tue, Jul 21, 2020 at 10:57:13AM +0200, Pali Rohár wrote: > On Wednesday 15 July 2020 17:21:08 Lorenzo Pieralisi wrote: > > On Wed, Jul 15, 2020 at 02:17:26PM +0200, Pali Rohár wrote: > > > On Monday 13 July 2020 12:23:25 Lorenzo Pieralisi wrote: > > > > On Mon, Jul 13, 2020 at 10:27:47AM +0200, Pali Rohár wrote: > > > > > On Friday 10 July 2020 10:18:00 Lorenzo Pieralisi wrote: > > > > > > On Thu, Jul 09, 2020 at 05:09:59PM +0200, Pali Rohár wrote: > > > > > > > > I understand that but the bridge bus resource can be trimmed to just > > > > > > > > contain the root bus because that's the only one where there is a > > > > > > > > chance you can enumerate a device. > > > > > > > > > > > > > > It is possible to register only root bridge without endpoint? > > > > > > > > > > > > It is possible to register the root bridge with a trimmed IORESOURCE_BUS > > > > > > so that you don't enumerate anything other than the root port. > > > > > > > > > > Hello Lorenzo! I really do not know how to achieve it. From code it > > > > > looks like that pci/probe.c scans child buses unconditionally. > > > > > > > > > > pci-aardvark.c calls pci_host_probe() which calls functions > > > > > pci_scan_root_bus_bridge() which calls pci_scan_child_bus() which calls > > > > > pci_scan_child_bus_extend() which calls pci_scan_bridge_extend() (bridge > > > > > needs to be reconfigured) which then try to probe child bus via > > > > > pci_scan_child_bus_extend() because bridge is not card bus. > > > > > > > > > > In function pci_scan_bridge_extend() I do not see a way how to skip > > > > > probing for child buses which would avoid enumerating aardvark root > > > > > bridge when PCIe device is not connected. > > > > > > > > > > dmesg output contains: > > > > > > > > > > advk-pcie d0070000.pcie: link never came up > > > > > advk-pcie d0070000.pcie: PCI host bridge to bus 0000:00 > > > > > pci_bus 0000:00: root bus resource [bus 00-ff] > > > > > > > > This resource can be limited to the root bus number only before calling > > > > pci_host_probe() (ie see pci_parse_request_of_pci_ranges() and code in > > > > pci_scan_bridge_extend() that programs primary/secondary/subordinate > > > > busses) but I think that only papers over the issue, it does not fix it. > > > > > > I looked at the code in pci/probe.c again and I do not think it is > > > possible to avoid scanning devices. pci_scan_child_bus_extend() is > > > unconditionally calling pci_scan_slot() for devfn=0 as the first thing. > > > And this function unconditionally calls pci_scan_device() which is > > > directly trying to read vendor id from config register. > > > > > > So for me it looks like that kernel expects that can read vendor id and > > > device id from config register for device which is not connected. > > > > Not if it is connected to a bus that the root port does not decode, > > that's what I am saying. > > > > > And trying to read config register would cause those timeouts in > > > aardvark. > > > > The root port (which effectively works as PCI bridge from this > > standpoint) does not issue config cycles for busses that aren't within > > its decoded bus range, which in turn is determined by the firmware > > IORESOURCE_BUS resource. > > > > This issue is caused by devices that are connected downstream to > > the root port. > > > > Anyway - patch merged > > Could you send me a link to git commit? I have looked into > lpieralisi/pci.git repository, but I do not see it here. Apologies - I did not push it out, I have pushed it out on pci/aardvark now. > > but I would be happy to keep this discussion going, somehow. > > Ok, no problem. As I said if anybody has any idea or would like to see > some tests from me, I can do it and provide results. Sounds good, I will let you know, thanks. Lorenzo > > If the LPC20 VFIO/IOMMU/PCI microconference is approved it can be a > > good venue for this to happen. > > > > Lorenzo
