On Fri, 2021-01-22 at 07:20 -0600, Bjorn Helgaas wrote: > On Fri, Jan 22, 2021 at 03:03:11PM +0800, Mingchuang Qiao wrote: > > On Thu, 2021-01-21 at 16:31 -0600, Bjorn Helgaas wrote: > > > [+cc Alex and Mingchuang et al from > > > https://lore.kernel.org/r/20210112072739.31624-1-mingchuang.qiao@xxxxxxxxxxxx] > > > > > > On Tue, Jan 19, 2021 at 04:14:10PM +0300, Mika Westerberg wrote: > > > > PCIe r5.0, sec 7.5.3.16 says that the downstream ports must reset the > > > > LTR enable bit if the link goes down (port goes DL_Down status). Now, if > > > > we had LTR previously enabled and the PCIe endpoint gets hot-removed and > > > > then hot-added back the ->ltr_path of the downstream port is still set > > > > but the port now does not have the LTR enable bit set anymore. > > > > > > > > For this reason check if the bridge upstream had LTR enabled previously > > > > and re-enable it before enabling LTR for the endpoint. > > > > > > > > Reported-by: Utkarsh H Patel <utkarsh.h.patel@xxxxxxxxx> > > > > Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> > > > > > > I think this and Mingchuang's patch, which is essentially identical, > > > are right and solves the problem for hot-remove/hot-add. In that > > > scenario we call pci_configure_ltr() on the hot-added device, and > > > with this patch, we'll re-enable LTR on the bridge leading to the new > > > device before enabling LTR on the new device itself. > > > > > > But don't we have a similar problem if we simply do a Fundamental > > > Reset on a device? I think the reset path will restore the device's > > > state, including PCI_EXP_DEVCTL2, but it doesn't do anything with the > > > upstream bridge, does it? > > > > Yes. I think the same problem exists under such scenario, and that’s the > > issue my patch intends to resolve. > > I also prepared a v2 patch for review(update the patch description). > > Shall I submit the v2 patch for review? > > How does your patch solve this for the reset path? I don't think we > call pci_configure_ltr() when we reset a device. > Sorry, I misunderstand the reset path. When we do a Fundamental Reset on a device, we can trigger device removal and rescan flow to restore the device. In device rescan flow, pci_configure_ltr() will be invoked. I regard the "remove and rescan flow" as a part of reset path for this case :) If we restore device just with pci_restore_state() in device driver after device resets, the LTR problem also exists due to pci_restore_state() does nothing with upstream bridge. In next patch, I would like to re-enable LTR for upstream bridge before restoring device's PCI_EXP_DEVCTL2 if it is needed. > > > So if a bridge and a device below it both have LTR enabled, can't we > > > have the following: > > > > > > - bridge LTR enabled > > > - device LTR enabled > > > - reset device, e.g., via Secondary Bus Reset > > > - link goes down, bridge disables LTR > > > - link comes back up, LTR disabled in both bridge and device > > > - restore device state, including LTR enable > > > - device sends LTR message > > > - bridge reports Unsupported Request > > > > > > > --- > > > > Previous version can be found here: > > > > > > > > https://lore.kernel.org/linux-pci/20210114134724.79511-1-mika.westerberg@xxxxxxxxxxxxxxx/ > > > > > > > > Changes from the previous version: > > > > > > > > * Corrected typos in the commit message > > > > * No need to call pcie_downstream_port() > > > > > > > > drivers/pci/probe.c | 17 ++++++++++++++++- > > > > 1 file changed, 16 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > > > > index 0eb68b47354f..a4a8c0305fb9 100644 > > > > --- a/drivers/pci/probe.c > > > > +++ b/drivers/pci/probe.c > > > > @@ -2153,7 +2153,7 @@ static void pci_configure_ltr(struct pci_dev *dev) > > > > { > > > > #ifdef CONFIG_PCIEASPM > > > > struct pci_host_bridge *host = pci_find_host_bridge(dev->bus); > > > > - struct pci_dev *bridge; > > > > + struct pci_dev *bridge = NULL; > > > > u32 cap, ctl; > > > > > > > > if (!pci_is_pcie(dev)) > > > > @@ -2191,6 +2191,21 @@ static void pci_configure_ltr(struct pci_dev *dev) > > > > if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT || > > > > ((bridge = pci_upstream_bridge(dev)) && > > > > bridge->ltr_path)) { > > > > + /* > > > > + * Downstream ports reset the LTR enable bit when the > > > > + * link goes down (e.g on hot-remove) so re-enable the > > > > + * bit here if not set anymore. > > > > + * PCIe r5.0, sec 7.5.3.16. > > > > + */ > > > > + if (bridge) { > > > > + pcie_capability_read_dword(bridge, PCI_EXP_DEVCTL2, &ctl); > > > > + if (!(ctl & PCI_EXP_DEVCTL2_LTR_EN)) { > > > > + pci_dbg(bridge, "re-enabling LTR\n"); > > > > + pcie_capability_set_word(bridge, PCI_EXP_DEVCTL2, > > > > + PCI_EXP_DEVCTL2_LTR_EN); > > > > + } > > > > + } > > > > + pci_dbg(dev, "enabling LTR\n"); > > > > pcie_capability_set_word(dev, PCI_EXP_DEVCTL2, > > > > PCI_EXP_DEVCTL2_LTR_EN); > > > > dev->ltr_path = 1; > > > > -- > > > > 2.29.2 > > > > > >
