Re: [Qemu-devel] [PATCH] pcie: fix device unplug timeout

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jul 23, 2019 at 07:48:00AM +0000, Zhangbo (Oscar) wrote:
> If the linux kernel only receives an ABP event during pcie unplug, it will sleep 5s 
> to expect a PDC event, which will cause device unplug timeout.

My understanding is that there's no timeout. Spec says:
	If present, the Power Indicator provides visual feedback to the human operator (if the system
	software accepts the request initiated by the Attention Button) by blinking. Once the Power
	Indicator begins blinking, a 5-second abort interval exists during which a second depression of the
	Attention Button cancels the operation.

this is exactly what linux implements.
Thus after an ABP event, linux starts a 5 second timer:
	schedule_delayed_work(&ctrl->button_work, 5 * HZ);


> In the meanwhile, if the kernel only receives a PDC event during the unplug, it
> will wait for at least 1 second before checking card present as data link layer
> state changed (link down) event reported prior to presence detect changed
> (card is not present).

I don't understand what you are saying exactly.
But I don't see any other delayed work in
drivers/pci/hotplug/pciehp_ctrl.c


> Therefore we can send both ABP and PDC events to the kernel in unplug process
> to avoid unplug timeout.
> 
> Signed-off-by: limingwang@huawei.com
> Signed-off-by: fangying1@huawei.com
> Signed-off-by: oscar.zhangbo@huawei.com

I see this in linux:

/**
 * pciehp_check_presence() - synthesize event if presence has changed
 *              
 * On probe and resume, an explicit presence check is necessary to bring up an
 * occupied slot or bring down an unoccupied slot.  This can't be triggered by
 * events in the Slot Status register, they may be stale and are therefore
 * cleared.  Secondly, sending an interrupt for "events that occur while
 * interrupt generation is disabled [when] interrupt generation is subsequently
 * enabled" is optional per PCIe r4.0, sec 6.7.3.4.
 */


My suggestion therefore is to try to clear Presence Detect State,
set presence detect changed and do not set attention button
pressed.


> ---
>  hw/pci/pcie.c         | 8 ++------
>  include/hw/pci/pcie.h | 1 -
>  2 files changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/hw/pci/pcie.c b/hw/pci/pcie.c
> index 174f392..a800f23 100644
> --- a/hw/pci/pcie.c
> +++ b/hw/pci/pcie.c
> @@ -485,7 +485,8 @@ void pcie_cap_slot_unplug_request_cb(HotplugHandler *hotplug_dev,
>                                       PCI_EXP_LNKSTA_DLLLA);
>      }
>  
> -    pcie_cap_slot_push_attention_button(PCI_DEVICE(hotplug_dev));
> +    pcie_cap_slot_event(PCI_DEVICE(hotplug_dev),
> +                        PCI_EXP_HP_EV_PDC | PCI_EXP_HP_EV_ABP);
>  }
>  
>  /* pci express slot for pci express root/downstream port
> @@ -701,11 +702,6 @@ int pcie_cap_slot_post_load(void *opaque, int version_id)
>      return 0;
>  }
>  
> -void pcie_cap_slot_push_attention_button(PCIDevice *dev)
> -{
> -    pcie_cap_slot_event(dev, PCI_EXP_HP_EV_ABP);
> -}
> -
>  /* root control/capabilities/status. PME isn't emulated for now */
>  void pcie_cap_root_init(PCIDevice *dev)
>  {
> diff --git a/include/hw/pci/pcie.h b/include/hw/pci/pcie.h
> index 8cf3361..0975a54 100644
> --- a/include/hw/pci/pcie.h
> +++ b/include/hw/pci/pcie.h
> @@ -112,7 +112,6 @@ void pcie_cap_slot_write_config(PCIDevice *dev,
>                                  uint16_t old_slt_ctl, uint16_t old_slt_sta,
>                                  uint32_t addr, uint32_t val, int len);
>  int pcie_cap_slot_post_load(void *opaque, int version_id);
> -void pcie_cap_slot_push_attention_button(PCIDevice *dev);
>  
>  void pcie_cap_root_init(PCIDevice *dev);
>  void pcie_cap_root_reset(PCIDevice *dev);
> -- 
> 1.8.3.1