On Sat, 2024-12-07 at 19:44 +0100, Niklas Schnelle wrote: > Trying to enable bwctrl on a Thunderbolt port causes a boot hang on some > systems though the exact reason is not yet understood. As per the spec > Thunderbolt PCIe Downstream Ports have a fake Max Link Speed of 2.5 GT/s > (USB4 v2 sec 11.2.1): > > "Max Link Speed field in the Link Capabilities Register set to 0001b > (data rate of 2.5 GT/s only). > Note: These settings do not represent actual throughput. > Throughput is implementation specific and based on the USB4 Fabric > performance." > > More generally if 2.5 GT/s is the only supported link speed there is no > point in throtteling as this is already the lowest possible PCIe speed > so don't advertise the capability stopping bwctrl from being probed on > these ports. > > Link: https://lore.kernel.org/linux-pci/Z1R4VNwCOlh9Sg9n@xxxxxxxxx/ > Fixes: 665745f27487 ("PCI/bwctrl: Re-add BW notification portdrv as PCIe BW controller") > Tested-by: Niklas Schnelle <niks@xxxxxxxxxx> > Signed-off-by: Niklas Schnelle <niks@xxxxxxxxxx> Should probably add but forgot: Suggested-by: Lukas Wunner <lukas@xxxxxxxxx> > --- > Note: This issue causes a boot hang on my personal workstation see the > Link for details. > --- > drivers/pci/pcie/portdrv.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c > index 5e10306b63081b1ddd13e0a545418e2a8610c14c..e5f80e4a11aad4ce60b2ce998b40ec9fda8c653d 100644 > --- a/drivers/pci/pcie/portdrv.c > +++ b/drivers/pci/pcie/portdrv.c > @@ -270,7 +270,8 @@ static int get_port_device_capability(struct pci_dev *dev) > u32 linkcap; > > pcie_capability_read_dword(dev, PCI_EXP_LNKCAP, &linkcap); > - if (linkcap & PCI_EXP_LNKCAP_LBNC) > + if (linkcap & PCI_EXP_LNKCAP_LBNC && > + (linkcap & PCI_EXP_LNKCAP_SLS) != PCI_EXP_LNKCAP_SLS_2_5GB) > services |= PCIE_PORT_SERVICE_BWCTRL; > } > > > --- > base-commit: 40384c840ea1944d7c5a392e8975ed088ecf0b37 > change-id: 20241207-fix_bwctrl_thunderbolt-bd1f96b3d98f > > Best regards,
