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SubjectRe: [PATCH] PCI: pciehp: Flush slot control prior to reset
On Fri, 2014-11-07 at 15:54 -0700, Alex Williamson wrote:
> Since 3461a068661c we don't automatically do a pcie_wait_cmd() for
> as part of pcie_write_cmd(), it needs to be called explicitly or
> triggered by the next pcie_write_cmd(). However, when we do a
> secondary bus reset and we're using pcie_write_cmd() to make sure
> that we don't see that bus reset as a hotplug event, we really want
> to make sure the update is complete. Testing on an old Lenovo S20
> system, which sets surprise hotplug for some slots, this failure to
> flush results in a link down event seen by the hotplug controller
> when we issue the bus reset and returns us to the undesireable
> behavior of removing and re-adding the device. Force a flush by
> adding an explicit call to pcie_wait_cmd().
> Signed-off-by: Alex Williamson <>
> Cc: [3.17]
> ---
> drivers/pci/hotplug/pciehp_hpc.c | 1 +
> 1 file changed, 1 insertion(+)
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 0ebf754..e540966 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -660,6 +660,7 @@ int pciehp_reset_slot(struct slot *slot, int probe)
> pci_pcie_cap(ctrl->pcie->port) + PCI_EXP_SLTCTL, 0);
> if (pciehp_poll_mode)
> del_timer_sync(&ctrl->poll_timer);
> + pcie_wait_cmd(ctrl);
> pci_reset_bridge_secondary_bus(ctrl->pcie->port);

I think we might need a similar change on the other side of the reset,
calling pcie_wait_cmd() explicitly before we re-enable polling. The
patch above passed about 7000 VM startup/shutdown cycles (up from zero
w/o the patch), but it did eventually get a spurious hotplug. With the
additional pcie_wait_cmd() I'm thinking about, I've passed 8000 cycles.
TL;DR, I'm probably sending a v2 of this patch. Thanks,


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