Re: [Qemu-devel] Re: [PATCH v6 07/12] pcie/hotplug: introduce pushing attention button command

[Isaku Yamahata]

On Fri, Oct 22, 2010 at 04:38:49PM +0200, Michael S. Tsirkin wrote:
> On Fri, Oct 22, 2010 at 01:35:47PM +0200, Markus Armbruster wrote:
> > "Michael S. Tsirkin" <address@hidden> writes:
> > 
> > > On Wed, Oct 20, 2010 at 05:18:56PM +0900, Isaku Yamahata wrote:
> > >> glue pcie_push_attention_button command.
> > >> 
> > >> Signed-off-by: Isaku Yamahata <address@hidden>
> > >
> > > So as a high level command, I think we need to
> > > think about how to tie this into pci_add/pci_del.
> > > Right?
> > [...]
> > 
> > Do we have consensus how our set of commands for hot plug should look
> > like?  We talked about it, but did we reach consensus?  If yes, did we
> > write it down somewhere?
> 
> I think for simple things yes:
> - command to send hotplug notification to the guest
> - command to immediately add/remove the device
> - event to notify about guest ack
> - way to poll status: did guest ack last command?

I'm not sure about guest ack. Let me check my understanding.
The current qemu pci hot plug has its own hot plug controler,
PIIX4_PM, which relies on ACPI.

- command to add the device into the slot
  This corresponds to physically inserting the device into the slot.
  - qemu pci hot plug case: device_add/pci_add command.
    The qemu pci hot plug controller, PIIX4_PM, detects the insertion,
    then notify the guest OS of the event via ACPI, _L01.
    The guest OS would start to probe the device.

  - pci express native hot plug case: device_add/pci_add command.
    The pcie hot plug controller detects the the insertion,
    then notify the guest OS of the event via interrupt.
    The guest OS would start to probe the device.

- command to remove the device from the slot
  This corresponds to physically removing the device from the slot.
  - qemu pci hot plug case: No corresponding command.
    There is no way to remove the pci card forcibly from the slot.

  - pci express native hot plug case: device_del/pci_del
    After the removal of the card, the hot plug controller notifies
    the guest OS via interrupt.

- command to send hotplug notification to the guest
  command to push attention button.
  This corresponds to pushing the button near the slot.
  - qemu pci hot plug case: device_del/pci_del command
    Maybe the button is called an eject button.
    When the button is pushed, the hot plug controller notifies
    the guest OS via ACPI, _L01.
    Then, guest OS reacts the event by calling ACPI \_SB.PCI0.S<n>._EJ0
    method. It program the hot plug controller to eject the device
    in the given slot. As a result, the device is removed from the slot.
    If the guest OS doesn't call _EJ0 (nor programs the controller directly),
    the device stays there.
    There is no way to remove the pci card without the guest OS
    intervention.

  - pci express native hot plug case:
    pcie_push_attention_button command with my patch series.
    The hot plug controller raise the interrupt to the guest OS.
    There is no specified action from the OS.

- a way to get the slot status
  new command for QMP/HMP? or enhance info pci?

- QMP event for qemu to notify the slot status change
  e.g. when LED status is changed, qmp event will be sent.

> Existing ones will keep function:
> - send notification and when acked remove device
> - add device and send notification
> These are useful for human monitor but maybe not
> for management.
> 
> 
> -- 
> MST
> 

-- 
yamahata