Re: [PATCH] PCI: pciehp: Ignore spurious link inactive change when off

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Apr 09, 2021 at 02:59:35PM -0600, Jon Derrick wrote:
> When a specific x8 CEM card is bifurcated into x4x4 mode, and the
> upstream ports both support hotplugging on each respective x4 device, a
> slot management system for the CEM card requires both x4 devices to be
> sysfs removed from the OS before it can safely turn-off physical power.
> The implications are that Slot Control will display Powered Off status
> for the device where the device is actually powered until both ports
> have powered off.
> 
> When power is removed from the first half, the link remains active to
> provide clocking while waiting for the second half to have power
> removed. When power is then removed from the second half, the first half
> starts shutdown sequence and will trigger a link status change event.
> This is misinterpreted as an enabling event due to positive presence
> detect and causes the first half to be re-enabled.
> 
> The spurious enable can be resolved by ignoring link status change
> events when no link is active when in the off state.
> 
> Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>

Applied to pci/hotplug for v5.14, thanks!

> ---
>  drivers/pci/hotplug/pciehp_ctrl.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> index 529c34808440..a2c5eef03e7d 100644
> --- a/drivers/pci/hotplug/pciehp_ctrl.c
> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> @@ -265,6 +265,11 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
>  		cancel_delayed_work(&ctrl->button_work);
>  		fallthrough;
>  	case OFF_STATE:
> +		if ((events & PCI_EXP_SLTSTA_DLLSC) && !link_active) {
> +			mutex_unlock(&ctrl->state_lock);
> +			break;
> +		}
> +
>  		ctrl->state = POWERON_STATE;
>  		mutex_unlock(&ctrl->state_lock);
>  		if (present)
> -- 
> 2.26.2
>