Messages in this thread | | | Date | Wed, 16 Aug 2023 18:48:35 +0530 | Subject | Re: [PATCH] PCI: Allocate maximum available buses to help extending the daisy chain | From | Sanath S <> |
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Adding Mika.
On 8/16/2023 10:49 AM, Sanath S wrote: > In the case of Thunderbolt, it contains a PCIe switch and one or > more hotplug-capable PCIe downstream ports where the daisy chain > can be extended. > > Currently when a Thunderbolt Dock is plugged in during S5/Reboot, > System BIOS allocates a very minimal number of buses for bridges and > hot-plug capable PCIe downstream ports to enumerate the dock during > boot. Because of this, we run out of bus space pretty quickly when > more PCIe devices are attached to hotplug downstream ports in order > to extend the chain. > > Before: > +-04.0 > +-04.1-[63-c1]----00.0-[64-69]--+-00.0-[65]-- > | +-01.0-[66]-- > | +-02.0-[67]-- > | +-03.0-[68]-- > | \-04.0-[69]-- > +-08.0 > > In case of a thunderbolt capable bridge, reconfigure the buses allocated > by BIOS to the maximum available buses. So that the hot-plug bridges gets > maximum buses and chain can be extended to accommodate more PCIe devices. > This fix is necessary for all the PCIe downstream ports where the daisy > chain can be extended. > > After: > +-04.0 > +-04.1-[63-c1]----00.0-[64-c1]--+-00.0-[65]-- > | +-01.0-[66-84]-- > | +-02.0-[85-a3]-- > | +-03.0-[a4-c0]-- > | \-04.0-[c1]-- > +-08.0 > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=216000 > Signed-off-by: Sanjay R Mehta <sanju.mehta@amd.com> > Signed-off-by: Sanath S <Sanath.S@amd.com> > --- > drivers/pci/probe.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > index 8bac3ce02609..ab7e90ef2382 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -1263,6 +1263,8 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev, > bool fixed_buses; > u8 fixed_sec, fixed_sub; > int next_busnr; > + int start = bus->busn_res.start; > + int end = bus->busn_res.end; > > /* > * Make sure the bridge is powered on to be able to access config > @@ -1292,6 +1294,13 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev, > broken = 1; > } > > + /* Reconfigure, If maximum buses are not allocated */ > + if (!pass && start != 0 && end != 0xff && subordinate != end) { > + pci_info(dev, "Bridge has subordinate 0x%x but max busn 0x%x, reconfiguring\n", > + subordinate, end); > + broken = 1; > + } > + > /* > * Disable Master-Abort Mode during probing to avoid reporting of > * bus errors in some architectures.
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