Re: [PATCH] PCI: pciehp: Don't enable slot unless link or presence up

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Mar 10, 2020 at 01:21:00PM -0500, Stuart Hayes wrote:
> When a pciehp slot is powered down via /sys/bus/pci/slots/<slot>/power,
> and then the card is physically removed, the kernel will sometimes try to
> enable the slot as the card is removed, which results in an error in the
> kernel log.
> 
> This can happen if the presence detect and link active bits don't go down
> at the exact same time. When the card is disabled via /sys/.../power, the
> card is placed in OFF_STATE, but the presence detect and link active bits
> can still be up.  Then, when, say, presence detect goes down, an interrupt
> reports that the presence detect has changed, and the code in
> pciehp_handle_presence_or_link_change() will see that the link is up
> (because it hasn't gone down yet), and it will try to enable the slot.
> 
> This patch modifies that code so it won't try to enable a slot in OFF_STATE
> unless it sees the presence detect changed bit with presence detect active,
> or the link status changed bit with an active link. This will prevent the
> unwanted attempts to enable a card that's being removed, but will still
> allow the slot to come up if the slot is re-enabled by writing to
> /sys/.../power, or if a new card is added to the slot.

Looking for a reviewed-by from Lukas for this.

> Signed-off-by: Stuart Hayes <stuart.w.hayes@gmail.com>
> ---
>  drivers/pci/hotplug/pciehp_ctrl.c | 24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> index 6503d15effbb..f6cbf21711e0 100644
> --- a/drivers/pci/hotplug/pciehp_ctrl.c
> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> @@ -267,16 +267,20 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
>  		cancel_delayed_work(&ctrl->button_work);
>  		/* fall through */
>  	case OFF_STATE:
> -		ctrl->state = POWERON_STATE;
> -		mutex_unlock(&ctrl->state_lock);
> -		if (present)
> -			ctrl_info(ctrl, "Slot(%s): Card present\n",
> -				  slot_name(ctrl));
> -		if (link_active)
> -			ctrl_info(ctrl, "Slot(%s): Link Up\n",
> -				  slot_name(ctrl));
> -		ctrl->request_result = pciehp_enable_slot(ctrl);
> -		break;
> +		if ((events & PCI_EXP_SLTSTA_PDC && present) ||
> +		    (events & PCI_EXP_SLTSTA_DLLSC && link_active)) {
> +			ctrl->state = POWERON_STATE;
> +			mutex_unlock(&ctrl->state_lock);
> +			if (present)
> +				ctrl_info(ctrl, "Slot(%s): Card present\n",
> +					  slot_name(ctrl));
> +			if (link_active)
> +				ctrl_info(ctrl, "Slot(%s): Link Up\n",
> +					  slot_name(ctrl));
> +			ctrl->request_result = pciehp_enable_slot(ctrl);
> +			break;
> +		}
> +		/* fall through */
>  	default:
>  		mutex_unlock(&ctrl->state_lock);
>  		break;
> -- 
> 2.18.1
>